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KEY CHARACTERISTICS OF EPIDEMIOLOGY Introduction to EPIDEMIOLOGY Population Focus Distribution Peter Duesberg...

KEY CHARACTERISTICS OF EPIDEMIOLOGY Introduction to EPIDEMIOLOGY Population Focus Distribution Peter Duesberg Determinants Exposures → Epidemiology is like a bikini; what is revealed is Outcomes interesting but what is hidden is crucial. Quantification Control of Health Problems WHY THE NEED FOR EPIDEMIOLOGY TO MEDICAL TECHNOLOGY? POPULATION FOCUS → To ensure optimal quality health care and → Ultimate focus is upon the occurrence of services in the diagnosis and treatment of health and diseases in population. diseases. → Population means “all the inhabitants of a given country or area considered IMPORTANCE OF EPIDEMIOLOGY together…” → Population approach contrasts with clinical Identification of diseases and their origin medicine’s concern with the individual -In depth knowledge of causes of certain (Population medicine) diseases (i.e., Cholera and salmonella) → Example: Salmonella outbreak and lung diseases Treatment and Prevention -It provides standards and protocols for Census Tracts termination of diseases → Investigations used to examine the Epidemic Detection occurrence of disease mortality across -It shows health trends throughout the years countries or among regional geographic subdivisions. Research DISTRIBUTION -It mainly focuses on constant discovery of better methods and medication to treat diseases → implies that the occurrence of diseases and other health outcomes varies in populations, SKILLS ACQUIRED THROUGH TRAINING IN EPIDEMIOLOGY with some subgroups of the populations more frequently than others. 1. Use of interdisciplinary approach → any factor that brings about change in a 2. Use of the scientific method health condition or other defined characteristics. 3. Enhancement of critical thinking ability TYPE OF DETERMINANTS a. Reasoning by analogy and deduction → Biological Agents b. Problem solving -Bacteria and viruses 4. Use of quantitative and computer methods → Chemical Agents -Toxic pesticides and chemical carcinogens 5. Communication skills → Stress 6. Inculcation of aesthetic values -Physical, emotional, and mental stress factors → Deleterious lifestyle practices EPIDEMIOLOGY -Sedentary life, smoking, and unhealthy eating → originates from Greek: epi (upon) + demos EXPOSURE (people) + logo (study of) → Concerned with the distribution and → pertain either to contact with a disease-causing determinants of health and diseases, morbidity, factor or to the amount of the factor that injuries, disability, and mortality in populations. impinges upon a group or individuals. → Studies here are applied to control health → Epidemiology searches for associations between problems in populations. exposures and health outcomes EXAMPLE OF EXPOSURES interacted with a host (the person who develops the disease) → Contact with infectious disease agents through consumption of contaminated foods. Agent → Biological agents or to forms of energy such as -exists in the environment radiation, noise, and extremes of temperature. → Environmental exposures to toxic chemicals, Pathogenesis potential carcinogens, or air pollution -occurs after the agent has interacted with a host OUTCOMES Epidemiological Transition → all possible results that may stem from exposure to a casual factor. -Shift in the patterns of morbidity and mortality → Range from specific infectious diseases to from causes related primarily to infectious disabling conditions, unintentional injuries, diseases and communicable diseases to causes chronic diseases, and other conditions associated with chronic, degenerative diseases. associated with personal behavior and lifestyle. Demographic Transition → Can be expressed as types and measures of: → Morbidity (illness due to a specific disease or -Shift from high births rates and death rates found health condition) in agrarian societies to much lower birth and → Mortality (cause of death) death rates in developed countries → Accurate clinical assessments of outcomes are important to the quality of epidemiological THREE TYPES OF PREVENTION research and the strength of inferences that can be made. Primary Prevention Secondary Prevention QUANTIFICATION Tertiary Prevention → Epidemiology is a quantitative discipline METHODS OF PREVENTION Quantification. → counting of cases of illness or other health  Creation of a healthful environment outcomes  Implementation of health education programs → Use of statistical measures to describe the  Administration of immunizations against specific occurrence of health outcomes as well as infectious diseases measures to measure their association with exposures. PRIMARY PREVENTION CONTROL OF HEALTH PROBLEMS → involves the prevention of disease before it → Aids with health promotion, alleviation of occurs. adverse health outcomes (infectious and chronic → Targets the stage of prepathogenesis and diseases), and prevention of disease. embodies general health promotion and specific → Epidemiological methods are applicable to the prevention against diseases. development of needs assessments, the design SECONDARY PRVENTION of prevention programs, and the evaluation of the success of such programs. → takes place during the early phases of → Epidemiology contributes to health policy pathogenesis and includes activities that limit the development by providing quantitative progression of disease. information that can be used by policy makers. → Example: Cancer screening COMMON TERMS Early detection of other chronic diseases Natural History of Disease TERTIARY PREVENTION -refers to the course of disease from its → directed toward the later stages of pathogenesis beginning to its final clinical endpoints and includes programs for restoring the patient’s Period of Prephatogenesis optimal functioning. → Example: Physical therapy for stroke victims and -time period in the natural history of disease fitness programs for recovering heart attack before a disease agent (e.g., bacterium) has patients  Aesthetic values are concerned with the appreciation of EVOLVING CONCEPTION OF beauty, which would seem to have no relevance to EPIDEMIOLOGY epidemiology. Nevertheless, you can hone your aesthetic Epidemiology is often considered to be a biomedical values by reading about the history of epidemiology and science that relies on a specific methodology and high- descriptions of epidemics and health problems found in level technical skills. Nevertheless, epidemiology in many literature. The writings of the great thinkers such as respects also is a "low-tech" science that can be Hippocrates and John Snow, who contributed so greatly appreciated by those who do not specialize in this field. to epidemiology, are compelling as works of literature. Many other writings relevant to epidemiology are extant. INTERDISCIPLINARY APPROACH DESCRIPTIVE EPIDEMIOLOGY Epidemiology is an interdisciplinary science, meaning that it uses information from many fields: -epidemiologic studies that are concerned with characterizing the amount and distribution of health and Mathematics disease within a population. Health outcomes are History classified according to the variables: Sociology Demography and geography ✓ Person (demographic characteristics such Behavioral sciences as sex, age, and race/ ethnicity) ✓ Place (denote geographic locations Law including a specific country or countries, USE OF SCIENTIFIC METHOD areas within countries, and places where localized patterns of disease may occur) Epidemiology is a scientific discipline that makes use of a ✓ Time (a decade, a year, a month, a week, or body of research methods like those used in the basic a day) sciences and applied fields including biostatistics. The work of the epidemiologist is driven by theories, -fundamental approach by epidemiologists, aim to hypotheses, and empirical data. The scientific method delineate the patterns and way disease occurs in employs a systematic approach and objectivity in populations. evaluating the results of research. Comparison groups are -focused on the development of hypotheses, set the used to examine the effects of exposures. Epidemiology stage for subsequent research that examines the uses rigorous study designs: cross- sectional, eco-logic, etiology of disease. case-control, and cohort. ENHANCEMENT OF CRITICAL THINKING ABILITY ANALYTICAL EPIDEMIOLOGY Critical thinking skills include the following: reasoning by anal-ogy, making deductions that follow from a set of -examines causal (etiologic) hypotheses regarding the evidence, and solving problems. We will learn that association between exposures and health conditions. epidemiologists use ana-logical reasoning to infer disease causality. -The field of analytic epidemiology proposes and evaluates causal models for etiologic associations and USE OF QUANTITATIVE AND COMPUTER METHODS studies them empirically. Biostatistics is one of the core disciplines of epidemiology. -"Etiologic studies are planned examinations of causality and the natural history of disease. Because of the close linkage between the two fields, epidemiology and biostatistics sometimes are housed in -These studies have required increasingly sophisticated the same academic department in some universities. analytic methods as the importance of low-level exposures is explored and greater refinement in COMMUNICATION SKILLS exposure-effect relationships is sought As a core discipline of public health, epidemiology is an -One approach of analytic epidemiology is to take applied field. Information from epidemiologic analyses advantage of naturally occurring situations or events in can be used to control diseases, improve the health of the order to test causal hypotheses. community, evaluate intervention programs, and inform public policy. NATURAL EXPERIMENTS -“naturally occurring circumstances in which subsets of the population have different levels of exposure to a supposed causal factor in a situation resembling an INCULCATION OF AESTHETIC VALUES actual experiment, where human subjects would be → He authored the historically important book On randomly allocated to groups” Airs, Waters, and Places. → Hippocrates' work and the writings of many of FOUNDATIONS OF EPIDEMIOLOGY the ancients did not delineate specific known agents involved in the causality of health Areas we cover: problems but referred more generically to air → Mercury- closest to the sun water, and food. → Venus- second planet from the sun QE RMIDDLE AGES (approx. 500 – 1450) → Jupiter- It’s a gas giant and a biggest planet. → Saturn- It is ringed one. It’s a huge gas giant. BLACK DEATH (1346- 1352) Milestones reached: → Great significance for epidemiology is the Black Death, which claimed up to one-third of the -Classical Antiquity (Before 500 AD) population of Europe at the time (20 to 30 million -Middle age (500-1450) out of 100 million people). → The Black Death was thought to be an epidemic -Renaissance (1200-1699) of bubonic plague, a bacterial disease caused by Yersinia pestis. -Eighteen Century (1700-1799) → Bubonic plague is characterized by painful -Nineteen Century (1800-1899) swellings of the lymph nodes (buboes) in the groin and elsewhere in the body; often include -Early Twentieth Century (1900-1939) fever and the appearance of black splotches on -Contemporary Era (1940- present) the skin. → Untreated, bubonic plague kills up to 60% of its victims. The bites of fleas harbored by rats and some other types of rodents can transmit plague. RENAISSANCE (approx. 1200 – 1699) PARACELSUS (1493- 1541) → Paracelsus was one of the founders of the field of toxicology, a discipline that is used to examine the toxic effects of chemicals found in environmental venues such as the workplace. → Active during the time of da Vinci and Copernicus, Paracelsus advanced toxicology during the early sixteenth century. → Among his contributions were several important concepts: the dose-response relationship, which refers to the observation THE PERIOD OF CLASSICAL ANTIQUITY (before 500 that the effects of a poison are related to the AD) strength of its dose, and the notion of target organ specificity of chemicals. HIPPOCRATES (460 BC – 370 BC) JOHN GRAUNT (1620-1674) → The ancient Greek authority Hippocrates contributed to epidemiology by departing from 1662 superstitious reasons for disease outbreaks. → John Graunt published Natural and Political → Until Hippocrates' time, supernatural Observations Mentioned in a Following Index explanations were used to account for the and Made Upon the Bills of Mortality. diseases that ravaged human populations. This work recorded descriptive 400 BC characteristics of birth and death data, including seasonal variations. infant → Hippocrates suggested that environmental mortality, and excess male over female factors such as water quality and the air were mortality. implicated in the causation of diseases.  Graunt is said to be the first to employ product. No wonder therefore that Potts observation has quantitative methods to de scribe come to be regarded as the foundation stone on which the population vital statistics by organizing knowledge of cancer prevention has been built! mortality data in a mortality table. In Pott's own words, Because of his contributions to vital statistics, Graunt has been called the... every body... is acquainted with the disorders to which Columbus of statistics. painters, plummers, glaziers, and the workers in white lead are liable; but there is a disease as peculiar to a EIGHTEENTH CENTURY (1700-1799) certain set of people which has not, at least to my knowledge, been publickly noteced; I mean the chimney- RAMAZZINI (1633-1714) sweepers' cancer. → Bernardino Ramazzini is regarded as the..The fate of these people seems singularly hard; in their founder (father) of the field of occupational early infancy, they are most frequently treated with great medicine. brutality, and almost starved with cold and hunger; they → He created elaborate descriptions of the are thrust up narrow, and sometimes hot chimnies, where manifestations of occupational diseases among they are bruised, burned, and almost suffocated; and many different types of workers. when they get to puberty, become peculiary [sic] liable to → His descriptions covered a plethora of a noisome, painful and fatal disease. Of this last occupations, from miners to cleaners of privies circumstance there is not the least doubt though perhaps to fabric workers. it may not have been sufficiently attended to, to make it → A pioneer in the field of ergonomics, by pointing generally known. Other people have cancers of the same out the hazards associated with postures part; and so have others besides lead-workers, the assumed in various occupations. Poictou colic, and the consequent paralysis; but it is → Ramazzini authored De Morbis Artificum nevertheless a disease to which they are particularly Diatriba (Diseases of Workers), published in liable; and so are chimney-sweepers to the cancer of the 1700. scrotum and testicles. The disease, in these people... → His book highlighted the risks posed by seems to derive its origin from a lodgment of soot in the hazardous chemicals, dusts, and metals used in rugae of the scrotum. the workplace. Following his conclusions about the relationship SIR PERCIVAL POTT (1714-1788) between scrotal cancer and chimney sweeping, → Sir Percival Pott, a London surgeon, is thought Pott established an occupational hygiene control to be the first individual to describe an measure the recommendation that chimney environmental cause of cancer. sweeps bathe once a week. 1775 EDWARD JENNER (1749-1823) → Pott made the astute observation that chimney 1798 sweeps had a high incidence of scrotal cancer → Jenner's findings regarding the development of a (in comparison with male workers in other vaccine that provided immunity to smallpox were occupations). published. ✓ He argued that chimney sweeps were prone → Jenner had observed that dairymaids who had to this malady as a consequence of their been infected with cowpox (transmitted by cattle) contact with soot. were immune to smallpox. ✓ In a book entitled Chirurgical Observations → The cowpox virus, known as the vaccinia virus, Relative to the Cataract, the Polypus of the produces a milder infection in humans than does Nose, the Cancer of the Scrotum, the the smallpox virus. Different Kinds of Ruptures, and the → Jenner created a vaccine by using material from Mortification of the Toes and Feet, Pott the arm of a dairymaid, Sarah Nelmes, who had developed a chapter called "A Short Treatise an active case of cowpox. of the Chimney Sweeper's Cancer." 1796 This brief work of only 725 words is noteworthy because ".. it provided the first clear description of an → the vaccine was injected into the arm of an eight- environmental cause of cancer, suggested a way to year-old boy, James Fipps, who was later prevent the disease, and led indirectly to the synthesis of exposed to smallpox and did not develop the the first known pure carcinogen and the isolation of the disease. first carcinogenic chemical to be obtained from a natural  → Concluding that the procedure was effective, → In addition, he explored the possible linkage Jenner vaccinated other children including his between mortality rates and population density, own son. showing that both the average number of deaths and births per 1,000 living persons increased with NINETEENTH CENTURY (1800-1899) population density (defined as number of persons per square mile). JOHN SNOW AND CHOLERA ROBERT KOCH (1843-1910) → Over the centuries, cholera has inspired great fear because of the dramatic symptoms and mortality → The German physician Robert Koch verified that that it causes. a human disease was caused by a specific living → Cholera is a potentially highly fatal disease marked organism. by profuse watery stools, called rice water stools. → He isolated the bacteria that cause anthrax → The onset of cholera is sudden and marked by (Bacillus anthracis) and cholera (Vibrio cholera). painless diarrhea that can progress to → One of his most famous contributions was dehydration and circulatory collapse; severe, identifying the cause of tuberculosis untreated cholera outbreaks can kill more than (Mycobacterium tuberculosis: this work was one-half of affected cases. described in 1882 in Die Aetiologie der → At present, the cause of cholera is known (the Tuberkulose. bacterium Vibrio cholera); the level of fatality is Koch's four postulates to demonstrate the often less than 1% when the disease is treated. association between a microorganism and a disease → One of the methods for transmission of cholera is were formatted as follows: through ingestion of contaminated water. → John Snow (1813-1858) was an English 1. The organism must be observed in every case of anesthesiologist who innovated several of the key the disease. epidemiologic methods that remain valid and in 2. It must be isolated and grown in pure culture. use today. 3. The pure culture must, when inoculated into a → For example, Snow believed that the disease susceptible animal, reproduce the disease. cholera was transmitted by contaminated water 4. The organism must be observed in, and and was able to demonstrate this association. recovered from, the experimental animals. → In Snow's time, the mechanism for the causation of infectious diseases such as cholera was EARLY TWENTIETH CENTURY (1900-1940) largely unknown. PANDEMIC INFLUENZA JOHN SNOW’S CONTRIBUTION: → Also known as the Spanish Flu, this pandemic ✓ Powers of observation and written expression raged from 1918 to 1919 and killed 50 to 100 ✓ Application of epidemiologic methods million persons globally. Mapping (spot maps) → Estimates suggest that one-third of the world's Use of data tables to describe infectious disease population, which then was 1.5 billion, became outbreaks. infected and developed clinically observable ✓ Participation in a natural experiment illness. ✓ Recommendation of a public health measure to → Instead of primarily attacking the young and the prevent diseases removal of the pump handle) elderly as is usually the situation with influenza, the Spanish Flu took a heavy toll on healthy WILLIAM FARR (1807-1883) young adults. → William Farr assumed the post of "Compiler of → One hypothesis is that the influenza virus interacted with respiratory bacteria, causing Abstracts" at the General Register Office (located numerous deaths from bacterial pneumonias. in England) in 1839 and held this position for forty → The death rate was so high that morgues were years. overflowing with bodies awaiting burial; → Among Farr's contributions to public health and adequate supplies of coffins and the services of epidemiology was the development of a more morticians were unavailable. sophisticated system for codifying medical → To handle the influx of patients, special field conditions than that which was previously in use. hospitals were set up. → Also noteworthy is the fact that Farr used data such as census reports to study occupational mortality in England. DISCOVERY OF PENICILLIN NEWER DEVELOPMENTS → Scottish researcher Alexander Fleming (1881- More recent contributions of epidemiology 1955) discovered the antimicrobial properties of include helping to discover the association the mold Penicillium no-tatum in 1928. This between the human papillomavirus and cervical breakthrough led to development of the antibiotic cancer, the correspondence between a penicillin, which became available toward the bacterium (Helico-bacter pylori) and peptic end of World War II. ulcers, and the correlation between genetic factors and cancers (e.g., breast cancer). CONTEMPORARY ERA (1940-PRESENT) BRIEF OVERVIEW OF CURRENT USES OF FRAMINGHAM STUDY EPIDEMIOLOGY → Begun in 1948, this pioneering research project Epidemiologists are indebted to J.N. Morris, who is named for Framingham, Massachusetts. published a list of seven uses of epidemiology; five of Initially, a random sample of 6,500 persons aged these uses are shown in the text box. 30 to 59 years participated. This project has been responsible for gathering basic information Among the principal uses of epidemiology are the about aspects of health such as the etiology of following: coronary heart disease. Historical use: study the history of the health of EPIDEMIC INTELLIGENCE SERVICE populations Community health use: diagnose the health → Alexander Langmuir was hired by the Centers of the community. for Disease Control and Prevention as the first Health services use: study the working of chief epidemiologist. One of Langmuir's health services contributions was the establishment in 1949 of Risk assessment use: estimate individuals the Epidemic Intelligence Service (EIS). In the risks of dis-ease, accident, or defect. beginning, the mission of EIS was to combat Disease causality use: search for the causes bioterrorism. Presently, EIS officers aid in the of health and disease rapid response to public health needs both domestically and internationally. HISTORICAL USE SMOKING AND HEALTH ✓ Epidemiological Transition → By the mid-twentieth century, a growing body of - Shift in the patterns of morbidity and mortality evidence suggested that cigarette smoking from causes related primarily to infectious contributed to early mortality from lung cancer as diseases and communicable diseases to causes well as other forms of morbidity and mortality. associated with chronic, degenerative diseases. → In 1964, the U.S. Surgeon General released Smoking and Health, IS which stated that ✓ Demographic Transition cigarette smoking is a cause of lung cancer in - Shift from high births rates and death rates men and is linked to other disabling or fatal found in agrarian societies to much lower birth diseases. and death rates in developed countries SMALLPOX ERADICATION COMMUNITY HEALTH USE → Jenner pioneered development of a smallpox Morris described this use as follows: "To diagnose the vaccine during the 1800s. Smallpox is an health of the community and the condition of the people, incurable disease caused by a virus. One form to measure the true dimensions and distribution of ill- of the virus variola major produces a highly fatal health in terms of incidence, prevalence, disability and infection in unvaccinated populations. mortality; to set health problems in perspective and define → Because of a highly effective surveillance and their relative importance; to identify groups needing vaccination program that was intensified during special attention. the late 1960s, the ancient scourge of smallpox was brought under control. The last known naturally acquired case was reported in Somalia in 1977. HEALTH SERVICES USE → Hence, it refers to the progression of a disease process in an individual over time, in the ✓ Operational Research absence of treatment. - translates knowledge of (changing) community → For example, untreated infection with HIV health and expectations in terms of needs for causes a spectrum of clinical problems services and measure (sic] how these are met. beginning at the time of seroconversion (primary -a type of study of the placement of health HIV) and terminating with AIDS and usually services in a community and the optimum death. utilization of such services HEALTH STATUS OF THE POPULATION ✓ Disease Management → Most diseases are caused by interaction between genetic and environmental factors. - Method of reducing healthcare cost by providing (Diabetes) integrated care for chronic conditions → Personal behaviors affect this interplay. → Epidemiology is used to study their influence ✓ Risk and the effects of preventive interventions - Probability that an event will occur, that an through health promotion. individual will become ill or die within a stated period of time or by a certain age, EVALUATION OF INTERVENTION ✓ Risk Factor -To evaluate the effectiveness and efficiency of health - Exposure that is associated with a disease, services. This means determining things such as: morbidity, mortality, or adverse health outcome. ✓ the impact of contraceptive use on population -Use risk assessment control ✓ -the value of treating high blood pressure DISEASE CASUALITY USE ✓ -the efficiency of sanitation measures to control Morris wrote “ To search for causes of health and disease diarrhea diseases. by computing the experience of groups defined by their composition, inheritance, and experience their behavior EPIDEMIOLOGY AND CLINICAL PRACTICE (sic) and environments. WHAT IS CLINICAL EPIDEMIOLOGY? ✓ John R. Paul coined the term "clinical epidemiology" in 1938, he defined it as “a SCOPE OF EPIDEMIOLOGY marriage between quantitative concepts used by epidemiologists to study disease in populations and decision-making in the individual case which WHAT IS EPIDEMIOLOGY? is the daily fare of clinical medicine." ✓ Clinical epidemiology is the study of the patterns, ✓ According to Last, J. (1988) "Epidemiology is the causes, and effects of health and disease in study of the distribution and determinants of patient populations and the relationships between health-related states or events in specified exposures or treatments and health outcomes. populations, and the application of this study for ✓ The science of making predictions about the prevention and control of health problems." individual patients by counting clinical events in CAUSATION OF DISEASE similar patients, using strong scientific methods for studies of groups of patients to ensure that the → Most diseases are caused by interaction predictions are accurate. between genetic and environmental factors. ✓ Clinical epidemiology is the use of quantitative (Diabetes) methods to clinical problems like disease → Personal behaviors affect this interplay. diagnosis, prognosis, and therapy. The field → Epidemiology is used to study their influence heavily relies on epidemiology and biostatistics and the effects of preventive interventions fundamentals, which are then utilized in a clinical through health promotion. setting to create an evidence base for therapeutic care. Concepts of validity and accuracy, metrics NATURAL HISTORY OF DISEASE of agreement and disagreement, and survival → Epidemiology is also concerned with the course analysis are further crucial methodological tools. and outcome (natural history) of diseases n These are employed to gauge the prevalence and individuals and groups. prognosis of diseases, evaluate the variability in  medical data, and create, validate, and use production and identification of valid tests, and to clinical scales and prediction rules. Intention-to- its logical extension. treat analysis, objective outcome measurement, NATURAL HISTORY OF DISEASE and randomization are all ideas that are used in clinical trials. → Refers to the progress in an individual over time, in the absence of medical intervention. This CLASSIC OR FIELD EPIDEMIOLOGY process starts from the moment of exposure of → Focused on evaluating the distribution and an individual to a causal agent that is capable of determinants of disease at the population level, causing disease. clinical epidemiology brings epidemiologic → Without medical intervention, the process end principles into the clinical setting to explore with: patterns, causes, and effects of health and ✓ Recovery disease at the patient level. ✓ Disability ✓ Death Clinical epidemiology encompasses a broad area of → Natural history of disease can be well investigation including. established by cohort study. → As these studies are costly and laborious, disease screening and prevention; identification understanding the natural history of disease is of risk and protective factors for disease. largely based on other epidemiological studies development of risk and prediction tools, and such as cross sectional and retrospective patient decision aids. studies. comparative effectiveness research of treatments; implementation of research findings and guidelines into the clinical setting GERIATRIC CLINICAL EPIDEMIOLOGY → Provides specific tools for understanding differences and overcoming challenges inherent to the conduct of research evaluating health and disease in older adults. → Training in geriatric clinical epidemiology, such as in our Training Program, equips clinician and non-clinician investigators with specialized tools to engage in clinical research on topics such as the multifactorial etiology of geriatric conditions, multiple chronic conditions, polypharmacy, and a focus on function and quality of life in addition to traditionally recognized clinical outcomes. TWO PHASES OF NATURAL HISTORY OF DISEASE: EVOLUTION OF CLINICAL EPIDEMIOLOGY PRE-PATHOGENESIS → Clinical epidemiology has performed a center → This is the period before the onset of disease role in 5 recent evolutions (some say (the agent has not yet entered man), but factors revolutions) on the healthcare area: evidence favoring its interaction with the human host are generation, critical evaluation, efficient storage already existing in the environment. and recovery, evidence-based medicine and PATHOGENESIS evidence synthesis. → This phase begins with entry of the disease WHY LEARN ABOUT CLINICAL EPIDEMIOLOGY? agent in the susceptible host (man) and it → Clinical epidemiology enables health multiplies there and causes disease. professionals to successfully implement a health ICEBERG PHENOMENON program or to deliver better health care to individuals or communities using evidence The iceberg phenomenon is a metaphor generated from research. coined in human medicine to describe a disease in which, → The basic aim of clinical epidemiology is to for every visibly affected individual, the population will promote the clinical observation and contain numerous others that are sub-clinically infected, interpretation methods, which result in valid carriers or undiagnosed clinical cases conclusions. Clinical epidemiology aims for the  the extrinsic factors that affect the agent and provide opportunity for the host to be exposed. → The environment represents the favorable conditions for an agent to cause a health event. → Environmental factors include physical features like geology or climate, biological factors like the presence of disease transmitting insects and socioeconomic factors like crowding, sanitation and access to health services. TIME → In the center of the triangle is time. This factor is less consistently used to represent one thing. EPIDEMIOLOGICAL TRIANGLE Time can represent the incubation period disease (the time between when the host is infected and → The epidemiological when symptoms start to represent), duration of triangle is made up of the illness or amount of time a person can be sick three components that before the disease has run its course and results contribute to the in death or recovery. It also can be used to spread of disease: an describe the period from an infection to the external agent, a host and an environment in threshold of an epidemic for a population. which the agent and the host meet. Between the vertices, scientists will often describe the center LEVELS OF PREVENTION of the triangle as representing time. Another way NATURAL HISTORY OF DISEASE to think of the triangle model is what (the agent), who (host), where (environment) and when (time) → Refers to the progression of disease process in an of health issues. individual over time, in the absence of intervention. THE AGENT → There are four stages in the natural history of a → It is the cause of health events. When it comes to disease. These are: Stage of susceptibility, stage infectious disease the agent is a microbe or what of pre-symptomatic (sub- clinical) disease, stage people typically think as germs. As epidemiology of clinical disease and stage of disability or death. has evolved to cover more public health issues STAGE OF SUSCEPTIBILITY beyond diseases, agents can also be represented as physical or chemical factors. → In this stage disease has not yet developed, but → Epidemiology triangle includes Bacteria, Viruses, the groundwork has been laid by the presence of Fungi, Protozoa, Chemical Contaminants, factors that favor its occurrence. Physical Forces → Example: unvaccinated child is susceptible to measles. THE HOST STAGE OF PRE-SYMPTOMATIC (SUB-CLINICAL → Is the organism which is exposed to and harbor’s DISEASE) a disease. In epidemiology the host is usually a human who gets sick but can also be an animal → In this stage there are no manifestations of the that acts as a carrier of disease but may or may disease, but pathologic changes (damages) have not present illness. The host also represents started to occur in the body. The disease can only symptoms of a disease or health issue. As the be detected through special tests since the signs CDC explains, a variety of factors intrinsic to the and symptoms of the disease are not present. host, sometimes called risk factors, can influence → Example: Detection of antibodies against HIV in an individual's exposure, susceptibility, or an apparently healthy person and Ova of response to a causative agent. intestinal parasite in the stool of apparently → Risk factor includes Opportunities for exposure, healthy children. Susceptibility and response. → The pre-symptomatic (sub-clinical) stage may lead to the clinical stage or may sometimes end in THE ENVIRONMENT recovery without development of any signs or → Completing the triangle used by epidemiology to symptoms. model the study of disease and health issues are THE CLINICAL STAGE LEVELS OF DISEASE PREVENTION → At this stage the person has developed signs → The major purpose investigating the and symptoms of the disease. The clinical epidemiology of diseases is to learn how to stage of different diseases differs in duration, prevent and control them. Disease prevention severity and outcome. the outcomes of this means to interrupt or slow the progression of stage may be recovery, disability or death. disease. Epidemiology plays a central role in disease prevention by identifying those Examples: modifiable causes. There are three levels of ✓ Common cold has a short and mild clinical stage prevention: and almost everyone recovers quickly. PRIMARY PREVENTION ✓ Polio has a severe clinical stage, and many patients develop paralysis becoming disabled for → The main objectives of primary prevention are the rest of their lives. promoting health, preventing exposure and ✓ Rabies has a relatively short preventing disease. Primary prevention keeps the but severe clinical stage and almost disease process from becoming established by always results in death. eliminating causes of disease or increasing ✓ Diabetes Mellitus has a relatively longer clinical resistance to disease. stage and eventually results in death if the patient → Primary prevention has 3 components. These are is not properly treated. health promotion, prevention of exposure, and prevention of disease. STAGE OF DISABILITY OR DEATH Health promotion- consists of general non-specific → Some diseases run their course and then resolve interventions that enhance health and the body's ability to completely either spontaneously or by treatment. resist disease. Improvement of socioeconomic status, In others the disease may result in a residual provision of adequate food, housing, clothing, and defect, leaving the person disabled for a short or education are examples of health promotion. longer duration. Still, other diseases will end in death. Disability is limitation of a person's Prevention of Exposure- is the avoidance of factors activities including his role as a parent, wage which may cause disease if an individual is exposed to earner, etc. them. examples can be provision of safe adequate water, proper excreta disposal, and vector control. Examples: Prevention of Disease- is the prevention of disease ✓ Trachoma may cause blindness. development after the individual has become exposed to ✓ Meningitis may result in blindness or the disease-causing factors. Immunization is an example deafness. Meningitis may also result in of prevention of disease. Immunization does not prevent death. an infectious organism from invading the immunized host ✓ A schematic diagram of the but does prevent it from establishing an infection. If we natural history of diseases and take measles vaccine, it will not prevent the virus from their expected outcomes entering to the body, but it prevents the development of infection/disease. SECONDARY PREVENTION → The objective of secondary prevention is to stop or slow the progression of disease so as to prevent or limit permanent damage. Secondary prevention can be achieved through detecting people who already have the dies as early as possible and treat them. It is carried out before the person is permanently damaged. Examples: ✓ Prevention of blindness from Trachoma ✓ early detection and treatment of breast cancer to prevent  its progression to the invasive -The bigger this group, the higher is the expected stage, which is the severe form of the disease. number of cases. -The duration of observation also affects the frequency TERTIARY PREVENTION of cases; the longer the observation period, the more cases can occur. → Is targeted towards people with permanent -Count does not contain these elements! damage or disability. Tertiary prevention is needed in some diseases because primary and RATIO secondary preventions have failed, and in others because primary and secondary prevention are → The value obtained by dividing one quantity by not effective. It has two objectives: another. Treatment to prevent further disability or → Rate, proportion and percentage are types of death and ratios. To limit the physical, psychological, → It consists of a numerator and a denominator. social, and financial impact of disability, thereby improving the quality of life. This can be done through rehabilitation, which is the retraining of the remaining functions for maximal effectiveness. → Example: When a person becomes blind due to vitamin A deficiency, tertiary prevention (rehabilitation) can help the blind or partly blind person learn to do gainful work and be economically self-supporting. Measures of Morbidity and Mortality Used in Epidemiology COUNT → The simplest and most frequently performed quantitative measure in epidemiology. → Refers merely to the number of cases of a disease or other health phenomenon being studied. → Count of No. cases of a disease is used for surveillance of infectious disease for early detection of outbreaks. several examples of counts are the number of: → cases of influenza reported in Westchester Country, NY, during January of a particular year. → traffic fatalities in the borough of Manhattan during a 24-hour period → participants screened positive in a hypertension screening program organized by an industrial plant in northern California. → college dorm residents who had mono → stomach cancer patients who were foreign born Limited values of counts -Number of persons with characteristic, e.g., cases of dengue hemorrhagic fever, depends on the size of the population at risk of the disease in an area. PROPORTION Crude death rate= (2,448,017/ 296, 410,404) 1,000 or 100,000= → It’s a type of ratio in which the numerator is part of the denominator; proportions may be 8.259 per 1,000 expressed as percentages. 825.9 per 100,000 MORTALITY RATE → Death of a particular disease/event in the total → Example: From 7,999 females aged 16 – 45 y, population (e.g., maternal mortality) 2,496 use modern contraceptive methods. → The proportion of those who use modern contraceptive methods = 2,496 / 7,999 x 100 = 31.2% RATE → Frequency of events, that occur in a defined time period, divided by the average population of risk. FATALITY RATE → Mortality among cases of a particular disease DEATH RATE → Mortality of all diseases among the total population Commonly Used Rates for Population Study CRUDE RATE → It is a type of rate that has not been modified to take account of any of the factors such as the demographic makeup of the population that may affect the observed rate. → The numerator consists of the frequency of a disease over a specific period of time, and the denominator is a unit size of population. → The denominator is also termed the reference population. Example: (either rate per 1,000 or 100,000 is used as the multiplier) Number of deaths in US during 2005 = 2,448,017 Population of US as of July 5, 2005, = 296, 410,404 PROPORTIONAL MORTALITY RATE (PMR) Measures of Association and Risk → It is the number of deaths within a population ✓ Relative risk (RR) due to a specific disease or cause divided by the ✓ Odds ratio (OR) total number of deaths in the population. ✓ Attributable risk (AR) RELATIVE RISK → Relative risk is a ratio of risk comparing two groups on the basis of their exposure status. PREVALENCE → Used to determine if a particular exposure increases or decreases risk or probability of → Number of existing cases of disease developing a disease. → Proportion of individuals in a population with → Exposures could be to chemical, microbial, disease or condition at a specific point of time physical or psychosocial stressors. Formula: Incidence in exposed group Incidence in un-exposed group → Relative risk can be calculated from cohort study data. Example of Prevalence: → Cohort studies follow groups of people defined by exposure status over time to see whether → The prevalence of hypertension (systolic BP > disease develops (or not) 95 mmHg) on May 1-2, 2009, in Lao men aged → Interpreting relative risk: 30-69 years in Xienglairkhok village was: ✓ If the relative risk is 1, there is no evidence of increased or decreased risk due to the exposure. ✓ If the relative risk is greater than 1, there is evidence of increased risk due to the exposure. ✓ If the relative risk is less than 1, there is evidence of decreased risk due to the exposure. INCIDENCE ODDS RATIO → Incidence of disease is the number of new cases → Odds ratio (or relative odds) is defined as a ratio of disease” of the odds of developing disease in exposed ✓ Defined place- often a particular persons to the odds of developing disease in un- geographic area (city, state) exposed persons. ✓ Population at risk → Odds ratios are similar to relative risk. ✓ Defined period of time ✓ May be expressed a percentage or other Formula: A/B ÷ C/D ratio (per thousand) Basic formula:  → Odds ratios are calculated from case-control → The degrees of freedom of a statistic depend on studies. the sample size: - A case-control study starts by identifying those ✓ A. When the sample size is small, there with and without disease absent other are only a few independent pieces of knowledge of the incidence of disease in the information, and therefore only a few underlying population. Then exposures are degrees of freedom. assessed in both cases and controls to examine ✓ B. When the sample size is large, there potential association with disease. are many independent pieces of → Interpreting odds ratio: information, and therefore many degrees ✓ If the odds ratio is 1, there is no of freedom. evidence of increased or decreased risk NOTE: due to the exposure. ✓ If the odds ratio is greater than 1, there Although degrees of freedom are closely related to is evidence of increased risk due to the sample size, they’re not the same thing. There are always exposure. fewer degrees of freedom than the sample size. ✓ If the odds ratio is less than 1, there is Example A of degree of freedom evidence of decreased risk due to the exposure. Imagine your roommate has a sweet tooth, so she’s ATTRIBUTE RISK thrilled to discover that your college cafeteria offers seven dessert options. One week, she decides that she wants to → Attributable risk is a measure of how much of the have a different dessert every day. disease risk is due to a certain exposure, after accounting for the background risk of disease (in By deciding to have a different dessert every day, your unexposed people). roommate is imposing a restriction on her dessert choices. → Attributable risk is determined by subtracting the On Monday, she can choose any of the seven desserts. risk of disease in the unexposed group from risk On Tuesday, she can choose any of the six remaining in the exposed group dessert options. On Wednesday, she can choose any of the five remaining options, and so on. By Sunday, she’s had all the dessert options except one. She doesn’t have any choice to make on Sunday since there’s only one option remaining. Due to her restriction, your roommate could only choose her dessert on six of the seven days. Her dessert choice was free to vary on these six days. In contrast, her dessert choice on the last day wasn’t free to vary; it depended on her dessert choices of the previous six days. Example B of degree of freedom Suppose I ask you to pick five integers that sum to 100. The requirement of summing to 100 is a restriction on your number choices. DEGREE OF FREEDOM For the first number, you can choose any integer you → Degrees of freedom, often represented by v or df, want. Whatever your choice, the sum of the five numbers is the number of independent pieces of can still be 100. This is also true of the second, third, and information used to calculate a statistic. It’s fourth numbers. calculated as the sample size minus the number You have no choice for the final number; it has only one of restrictions. possible value and it isn’t free to vary. For example, → Degrees of freedom are normally reported in imagine you chose 15, 27, 42, and 3 as your first four brackets beside the test statistic, alongside the numbers. For the numbers to sum to 100, the final number results of the statistical test. needs to be 13. Due to the restriction, you could only choose four of the are parameters that are estimated as five numbers. The first four numbers were free to vary. In intermediate steps in calculating the statistic. contrast, the fifth number wasn’t free to vary; it depended n−r on the other four numbers. Where: Degrees of Freedom and Hypothesis Testing n is the sample size → The degrees of freedom of a test statistic determines the critical value of the hypothesis r is the number of restrictions, usually test. The critical value is calculated from the null the same as the number of parameters distribution and is a cut-off value to decide estimated whether to reject the null hypothesis. Test-specific formulas Student’s t distribution → To perform a t test, you calculate t for the sample and compare it to a critical value. To find the right critical value, you need to use the Student’s t distribution with the appropriate degrees of freedom. The null distribution of Student’s t changes with the degrees of freedom: When df = 1, the distribution is strongly leptokurtic, meaning the probability of extreme values is greater than in a normal distribution. As the df increases, the distribution becomes narrower and less leptokurtic. It becomes increasing similar to a standard normal distribution When df ≥ 30, Student’s t distribution is almost the same as a standard normal distribution. If you have a sample size of greater than 30, you can use the standard normal distribution (also known as the z distribution) instead of Student’s t distribution. CONFIDENCE INTERVAL POINT ESTIMATE → Use a single statistic based on sample data to estimate a population parameter. → Simplest approach → But not always very precise due to variation in the sampling distribution CONFIDENCE INTERVAL → Are used to estimate the unknown population mean. How to calculate degrees of freedom Formula: The degrees of freedom of a statistic is the sample size minus the number of estimate + margin of error restrictions. Most of the time, the restrictions CONFIDENCE LEVEL CONFIDENCE INTERVAL FOR A POPULATION MEAN: → Is the success rate of the method used to construct the interval. → Using this method, % of the time the intervals constructed will contain the true population parameter. What does it mean to be 95% confident? → 95% chance that m is contained in the confidence interval. → The probability that the interval contains m is 95% → The method used to construct the interval will produce intervals that contain μ 95% of the time. CRITICAL VALUE STEPS FOR DOING CONFIDENCE INTERVAL: → Found from the confidence level. → The upper z-score with probability p lying to its 1) Assumptions – right under the standard normal curve. SRS from population CONFIDENCE Tail Area Z* Sampling distribution is normal (or LEVEL approximately normal) 90%.05 1.645 95%.025 1.96 Given (normal) 99%.005 2.576 Large sample size (approximately normal) Graph data (approximately normal) σ is known 2) Calculate the interval. 3) Write a statement about the interval in the context of the problem.  FIND A SAMPLE SIZE: → If a certain margin of error is wanted, then to find the sample size necessary for that margin of error use: → Always round up to the nearest person! The heights of WHS male students are normally distributed with σ = 2.5 inches. How large a sample is necessary to be accurate within +.75 inches with a 95% confidence interval? What happens to the interval as the confidence level increases? → n = 43 → the interval gets wider as the confidence level In a randomized comparative experiment on the effects increases. of calcium on blood pressure, researchers divided 54 healthy, white males at random into two groups, takes How can you make the margin of error smaller? calcium or placebo. The paper reports a mean seated systolic blood pressure of 114.9 with standard deviation z* smaller of 9.3 for the placebo group. Assume systolic blood (lower confidence level) pressure is normally distributed. σ smaller  Can you find a z-interval for this problem? Why or why not? (less variation in the population) Student’s t- distribution n larger → Developed by William Gosset (To cut the margin of error in half, n → Continuous distribution must be 4 times as big) → Unimodal, symmetrical, bell-shaped density curve → Above the horizontal axis → Area under the curve equals 1 A random sample of 50 WHS students was taken, and → Based on degrees of freedom their mean SAT score was 1250. (Assume σ = 105) What is a 95% confidence interval for the mean SAT Graph examples of t- curves vs normal curve scores of WHS students? → We are 95% confident that the true mean SAT score for WHS students is between 1220.9 and 1279.1. Suppose that we have this random sample of SAT scores: 1130 1260 1090 1310 1420 1190 What is a 95% confidence interval for the true mean SAT score? (Assume σ = 105) → We are 95% confident that the true mean SAT score for WHS students is between 1115.1 and 1270.6. How does t compare to normal? → Shorter & more spread out. → More area under the tails → As n increases, t-distributions become more like a standard normal distribution. How to find t* Use Table B for t distributions. Look up confidence level at bottom & df on the sides. df = n – 1 Find these t* 90% confidence when n = 5 t* =2.132 95% confidence when n = 15 t* =2.145 ROBUST → An inference procedure is ROBUST if the confidence level or p-value doesn’t change much if the assumptions are violated. → t-procedures can be used with some skewness, as long as there are no outliers. → Larger n can have more skewness. Assumptions for t-interval Have an SRS from population. σ unknown Normal distribution – Given Another medical researcher claims that the true mean pulse rate for adults is 72 beats per minute. Does the – Large sample size evidence support or refute this? Explain. – Check graph of data → The 95% confidence interval contains the claim of 72 beats per minute. Therefore, there is no evidence to doubt the claim.  ▶ example: Chi-square goodness of fit test You’re hired by a dog food company to help them test three new dog food flavors. You recruit a random sample of 75 dogs and offer each dog a choice between the three flavors by placing bowls in front of them. You expect that the flavors will be equally popular among the dogs, with about 25 dogs choosing each flavor. Once you have your experimental results, you plan to use a chi-square goodness of fit test to figure out whether the distribution of the dogs’ flavor choices is significantly different from your expectations. What is the chi-square goodness of fit test? ▶ A chi-square (Χ2) goodness of fit test is a goodness of fit test for a categorical variable. Goodness of fit is a measure of how well a statistical model fits a set of observations. When goodness of fit is high, the values expected based on the model are close to the observed values. When goodness of fit is low, the values expected based on the model are far from the observed values. In Hypothesis testing Some Cautions: ▶ The chi-square goodness of fit test is a hypothesis test. It allows you to draw → The data MUST be a SRS from the population conclusions about the distribution of → The formula is not correct for more complex a population based on a sample. Using the chi- sampling designs, i.e., stratified, etc. square goodness of fit test, you can test whether → No way to correct for bias in data. the goodness of fit is “good enough” to conclude Cautions continued: that the population follows the distribution. → Outliers can have a large effect on confidence interval. → Must know σ to do a z-interval – which is unrealistic in practice. CHI- SQUARE GOODNESS OF FIT TEST ▶ A chi-square (Χ2) goodness of fit test is a type of Pearson’s chi-square test. ▶ Can use it to test whether the observed distribution of a categorical variable differs from your expectations.  How to calculate the test statistic (formula) Chi-square goodness of fit test hypothesis ▶ a chi-square goodness of fit test evaluates two hypotheses: the null and alternative hypotheses. They’re two competing answers to the question “Was the sample drawn from a population that follows the specified distribution?” Null hypothesis (H0): The population follows the specified distribution. Alternative hypothesis (Ha): The population does not follow the specified distribution. Example: Null and alternative hypothesis ▶ Null hypothesis (H0): The dog population chooses the three flavors in equal proportions (p1 = p2 = p3). ▶ Alternative hypothesis (Ha): The dog population does not choose the three flavors in equal proportions. When to use the chi-square goodness of fit test ▶ The following conditions are necessary if you want to perform a chi-square goodness of fit test: 1. You want to test a hypothesis about the distribution of one categorical variable. If your variable is continuous, you can convert it to a categorical variable by separating the observations into intervals. This process is known as data binning. 2. The sample was randomly selected from the population. 3. There are a minimum of five observations expected in each group.  Step 5: Decide whether the reject the null hypothesis If the Χ2 value is greater than the critical value, then the difference between the observed and expected distributions is statistically significant (p < α). The data allows you to reject the null hypothesis and provides support for the alternative hypothesis. If the Χ2 value is less than the critical value, then the difference between the observed and expected distributions is not statistically How to perform the chi-square goodness of significant (p > α). fit test The data doesn’t allow you to reject the null ▶ Step 1: Calculate the expected frequencies hypothesis and doesn’t provide support for the alternative hypothesis. ▶ Step 2: Calculate chi-square ▶ Step 3: Find the critical chi-square value o find the critical chi-square value, you’ll need to know two things: The degrees of freedom (df): For chi-square goodness of fit tests, the df is the number of groups minus one. Significance level (α): By convention, the significance level is usually.05. Example: Finding the critical chi-square value Since there are three groups (Garlic Blast, Blueberry Delight, and Minty Munch), there are two degreeds of freedom.