Epidemiology and Biostatistics PDF

EPIDEMOLIOGY AND BIOSTATISTICS What is the concept of epidemiology? Topic 1: A Public Health Approach Epidemiology is a population science that underpins health improvement and health care, Public...

EPIDEMOLIOGY AND BIOSTATISTICS What is the concept of epidemiology? Topic 1: A Public Health Approach Epidemiology is a population science that underpins health improvement and health care, Public health approach and how it relates to and is concerned with the pattern, frequency, public health core sciences. trends, and causes of disease. Public Health Core Sciences Its applications to population health research, Prevention Effectiveness policy-making, health service planning, health Epidemiology promotion, and clinical care. Laboratory Informatics Surveillance HISTORY OF EPIDEMIOLOGY Public Health The Beginnings Definition of Epidemiology Epidemiology’s roots are nearly 2,500 years - Comes from the Greek words old Epi – meaning on or upon As a discipline has blossoms since World War Demos - meaning people II Logos – meaning the study of Epidemiologic thinking has been traced from Hippocrates through John Graunt, William Farr, Epidemiology John Snow, and other - Study of the distribution and determinants of health-related states or 400 B.C events in specified populations, and the application of this to the control of health Hippocrates attempted to explain disease problems occurrence a rational rather than a - Is a scientific discipline with sound methods supernatural viewpoint of scientific inquiry as its foundation - Is often describes as the “basic science of public health” 1662 - Cinderella of the medical sciences John Graunt, a London haberdasher and councilman published a landmark analysis of Epidemiology Purposes in Public Health mortality data Practice This publication was the first to quantify 1. Discover the agent, host, and patterns of birth, death, and disease environmental factors that affect health occurrence, noting disparities between males 2. Determine the relative importance of and females, high infant mortality, urban/rural causes of illness, disability, and death differences, and seasonal variations 3. Identify those segments of the population that have the greatest risk from specific causes of ill health 1800 4. Evaluate the effectiveness of health programs and services in improving William Farr built upon Graunt’s work by population health systematically collecting and analyzing Britain’s mortality statistics Considered the father of modern vital statistics World War II has seen an explosion in the and surveillance development of research methods and the theoretical underpinnings of epidemiology Developed many of the basic practices used today in vital statistics and disease Epidemiology has been applied to the entire classification range of health-related outcomes, behaviors, and even knowledge and attitudes 1854 World War II John Snow, an anesthesiologist, considered the “FATHER OF FIELD EPIDEMIOLOGY.” Studies by Doll and Hill linking lung cancer to smoking and the study of cardiovascular Conducted studies of cholera outbreaks both to disease among residents of Framingham, discover the cause of disease and to prevent Massachusetts are two examples of how its recurrence pioneering researchers have applied He began his investigation by determining epidemiologic methods to chronic disease where in this area persons with cholera lived since World War II and worked. He marked each residence on a map of the area 1960s and Early 1970s Today, this type of map, showing the geographic distribution of cases, is called a Health workers applied epidemiologic methods spot map. to eradicate naturally occurring smallpox worldwide. This was an achievement in applied epidemiology of unprecedented proportions 1980s Epidemiology was extended to the studies of injuries and violence. In the 1990s, the related fields of molecular and genetic epidemiology (expansion of epidemiology to look at specific pathways, molecules and genes that influence risk of developing disease) took root Infectious diseases continued to challenge epidemiologists as new infectious agents Spot map of deaths from cholera in Golden emerged (Ebola virus, Human Square area, London, 1854 (redrawn from Immunodeficiency virus (HIV)/ Acquired original) Immunodeficiency Syndrome (AIDS), were identified (Legionella, Severe Acute Respiratory Syndrome (SARS), or changed 19th and 20th Centuries (drug-resistant Mycobacterium tuberculosis, Epidemiological methods began to be applied Avian influenza) in the investigation of disease occurrence 1930s and 1940s, epidemiologists extended their methods to noninfectious diseases  1990s changes in the character of disease, and its picture in other countries. Accelerating after the terrorist attacks of September 11, 2001, epidemiologists have had 6. In identifying syndromes from the to consider not only natural transmission of distribution of clinical phenomena infectious organisms but also deliberate spread among sections of the population. through biologic warfare and bioterrorism 7. In the search for causes of health and disease, starting with the discovery of USES OF EPIDEMIOLOGY groups with high and low rates, studying 1. Assessing the community’s health these differences in relation to 2. Making individual decisions differences in ways of living; and, where 3. Completing the clinical picture possible, testing these notions in the 4. Searching for causes actual practice among populations. USES OF EPIDEMIOLOGY (from US State ACCORDING TO Morris JN…. Department) 1. In historical study of the health of the - Count health-related events community and of the rise and fall of - Describe the distribution of health- diseases in the population; useful related events in the population ‘projections' into the future may also be - Describe clinical patterns possible. - Identify risk factors for developing 2. For community diagnosis of the diseases presence, nature and distribution of - Identify causes or determinants of health and disease among the disease population, and the dimensions of these - Identify control and/or preventive in incidence, prevalence, and mortality; measures taking into account that society is - Establish priorities for allocating changing and health problems are resources changing. - Select interventions for prevention and control 3. To study the workings of health services. - Evaluate programs This begins with the determination of - Conducts research: risk factors and needs and resources, proceeds to causes, drug trials/vaccine trials, analysis of services in action and, finally, operational research attempts to appraise. Such studies can be comparative between various populations. TERMINOLOGIES IN EPIDEMIOLOGY (basic) 4. To estimate, from the common AGENT. A factor, such as a microorganism, experience, the individual's chances and chemical substance, or form of radiation, risks of disease. whose presence, excessive presence, or (in deficiency diseases) relative absence is 5. To help complete the clinical picture by essential for the occurrence of a disease. including all types of cases in proportion; by relating clinical disease to the ANALYTIC EPIDEMIOLOGY. The aspect of subclinical; by observing secular epidemiology concerned with the search for health-related causes and effects. Uses prospective study. A group of people born comparison groups, which provide baseline during a particular period or year is called a data, to quantify the association between birth cohort. exposures and outcomes, and test hypotheses COHORT STUDY. A type of observational about causal relationships analytic study. Enrollment into the study is ANALYTIC STUDY. A comparative study based on exposure characteristics or intended to identify and quantify associations, membership in a group. Disease, death, or test hypotheses, and identify causes. Two other health-related outcomes are then common types are cohort study and case- ascertained and compared. control study CONTACT. Exposure to a source of an APPLIED EPIDEMIOLOGY. The application or infection, or a person so exposed. practice of epidemiology to address public CONTAGIOUS. Capable of being transmitted health issues. from one person to another by contact or close BIAS. Deviation of results or inferences from proximity the truth, or processes leading to such CONTROL. In a case-control study, systematic deviation. Any trend in the comparison group of persons without disease. collection, analysis, interpretation, publication, or review of data that can lead to conclusions DISTRIBUTION. In epidemiology, the that are systematically different from the truth. frequency and pattern of health-related characteristics and events in a population. In CASE. In epidemiology, a countable instance statistics, the observed or theoretical frequency in the population or study group of a particular of values of a variable. disease, health disorder, or condition under investigation. Sometimes, an individual with the ENDEMIC DISEASE. The constant presence particular disease. of a disease or infectious agent within a given geographic area or population group; may also CASE-CONTROL STUDY. A type of refer to the usual prevalence of a given disease observational analytic study. Enrollment into within such area or group. the study is based on presence (“case”) or absence (“control”) of disease. Characteristics EPIDEMIC. The occurrence of more cases of such as previous exposure are then compared disease than expected in a given area or between cases and controls. among a specific group of people over a particular period of time. CAUSE OF DISEASE. A factor (characteristic, behavior, event, etc.) that directly influences PANDEMIC. An epidemic occurring over a very the occurrence of disease. A reduction of the wide area (several countries or continents) and factor in the population should lead to a usually affecting a large proportion of the reduction in the occurrence of disease. population. CENSUS. The enumeration of an entire GRAPH. A way to show quantitative data population, usually with details being recorded visually, using a system of coordinates. on residence, age, sex, occupation, ethnic group, marital status, birth history, and HOST. A person or other living organism that relationship to head of household. can be infected by an infectious agent under natural conditions. COHORT. A well-defined group of people who have had a common experience or exposure, IMMUNITY, ACTIVE. Resistance developed in who are then followed up for the incidence of response to stimulus by an antigen (infecting new diseases or events, as in a cohort or agent or vaccine) and usually characterized by RATE. An expression of the frequency with the presence of antibody produced by the host. which an event occurs in a defined population. IMMUNITY, HERD. The resistance of a group RISK. The probability that an event will occur, to invasion and spread of an infectious agent, e.g. that an individual will become ill or die based on the resistance to infection of a high within a stated period of time or age. proportion of individual members of the group. RISK FACTOR. An aspect of personal The resistance is a product of the number behavior or lifestyle, an environmental susceptible and the probability that those who exposure, or an inborn or inherited are susceptible will come into contact with an characteristic that is associated with an infected person. increased occurrence of disease or other INFECTIVITY. The proportion of persons health-related event or condition. exposed to a causative agent who become SAMPLE. A selected subset of a population. A infected by an infectious disease sample may be random or non-random and it MORBIDITY. Any departure, subjective or may be representative or non-representative. objective, from a state of physiological or SECONDARY ATTACK RATE. A measure of psychological well-being. the frequency of new cases of a disease MORTALITY RATE. A measure of the among the contacts of known cases. frequency of occurrence of death in a defined SPOT MAP. A map that indicates the location population during a specified interval of time. of each case of a rare disease or outbreak by a NATURAL HISTORY OF DISEASE. The place that is potentially relevant to the health temporal course of disease from onset event being investigated, such as where each (inception) to resolution. case lived or worked. OUTBREAK. Synonymous with epidemic. TRANSMISSION OF INFECTION. Any mode Sometimes the preferred word, as it may or mechanism by which an infectious agent is escape sensationalism associated with the spread through the environment or to another word epidemic. Alternatively, a localized as person. opposed to generalized epidemic. TREND. A long-term movement or change in POPULATION. The total number of inhabitants frequency, usually upwards or downwards. of a given area or country. In sampling, the UNIVERSAL population may refer to the units from which PRECAUTIONS. Recommendations issued by the sample is drawn, not necessarily the total CDC to minimize the risk of transmission of population of people. bloodborne pathogens, particularly HIV and PUBLIC HEALTH SURVEILLANCE. The HBV, by health care and public safety workers. systematic collection, analysis, interpretation, Barrier precautions are to be used to prevent and dissemination of health data on an ongoing exposure to blood and certain body fluids of all basis, to gain knowledge of the pattern of patients. disease occurrence and potential in a VECTOR. An animate intermediary in the community, in order to control and prevent indirect transmission of an agent that carries disease in the community. the agent from a reservoir to a susceptible RANGE. In statistics, the difference between host. the largest and smallest values in a distribution. VEHICLE. An inanimate intermediary in the In common use, the span of values from indirect transmission of an agent that carries smallest to largest. the agent from a reservoir to a susceptible - surveillance relies on simple systems to host. collect a limited amount of information about each case. VITAL STATISTICS. Systematically tabulated information about births, marriages, divorces, and deaths, based on registration of these vital Disease surveillance usually begins events. with descriptive epidemiology – ZOONOSES. An infectious disease that is defining the what, who, when and where of transmissible under normal conditions from health-related events animals to humans. What - Define the disease events and/or its determinants What are the main objectives of Who - Descriptions of demographic epidemiology? characteristics are helpful in determining which groups are at risk for some outcome. The 1. The principal aim of epidemiology is to demographic characteristics usually include identify factors related to the occurrence age, sex and race/ethnicity. Other categories of disease. include socioeconomic status, history of 2. Identification of these factors both occupation, or smoking habits, which provide causal (causation) and risk factors, useful information about exposures that may enable developing a rational basis for present a risk. A history of underlying diseases prevention (epidemiology, prevention). may be useful for determining susceptibility to certain conditions Five major tasks of epidemiology in public When - Following changes in disease rates health practice over time, following long-term disease trends and knowledge of the seasonality of certain - Public health surveillance diseases helps identify unusual occurrences - Field investigation that may define epidemics. Temporal - Analytic studies associations between particular exposures on - Evaluation illness give information about incubation - Linkages periods and exposures posing a risk to others. Where - Insight into the geographical extent of Public health surveillance health-related events gives an idea of where the agent that causes a disease normally lives The ongoing, systematic collection, analysis, and multiplies, what may carry or transmit it interpretation, and dissemination of health data and how it spreads to help guide public health decision making and action. Surveillance Cycle Purpose Purpose of public health surveillance, which is sometimes called “information for action,” is to portray the ongoing patterns of disease occurrence and disease potential so that investigation, control, and prevention measures can be applied efficiently and effectively.  Field Investigation Analysis Objective of an investigation may simply be to Analysis begins with describing the learn more about the natural history, clinical characteristics of the subjects. It progresses to spectrum, descriptive epidemiology, and risk calculation of rates, creation of comparative factors of the disease before determining what tables (e.g., two-by-two tables), and disease intervention methods might be computation of measures of association (e.g., appropriate risk ratios or odds ratios), tests of significance (e.g., chi-square test), confidence intervals, Often lead to the identification of additional and the like. Many epidemiologic studies unreported or unrecognized ill persons who require more advanced analytic techniques might otherwise continue to spread infection to such as stratified analysis, regression, and others modeling. For some diseases, investigations may identify a source or vehicle of infection that can be controlled or eliminated Interpretation Involves putting the study findings into perspective, identifying the key take-home Analytic Studies messages, and making sound Hallmark of an analytic epidemiologic study is recommendations. Doing so requires that the the use of a valid comparison group epidemiologist be knowledgeable about the subject matter and the strengths and Epidemiologists must be skilled in all aspects weaknesses of the study. of such studies, including design, conduct, analysis, interpretation, and communication of findings. Evaluation Involves putting the study findings into Design perspective, identifying the key take-home messages, and making sound includes determining the appropriate research recommendations. Doing so requires that the strategy and study design, writing justifications epidemiologist be knowledgeable about the and protocols, calculating sample sizes, subject matter and the strengths and deciding on criteria for subject selection (e.g., weaknesses of the study. developing case definitions), choosing an appropriate comparison group, and designing may focus on plans (formative evaluation), questionnaires. operations (process evaluation), impact (summative evaluation), or outcomes — or any combination of these. Conduct Involves securing appropriate clearances and Purpose of Evaluation approvals, adhering to appropriate ethical principles, abstracting records, tracking down Effectiveness refers to the ability of a program and interviewing subjects, collecting and to produce the intended or expected results in handling specimens, and managing the data the field; effectiveness differs from efficacy, which is the ability to produce results under ideal conditions. Efficiency refers to the ability of the program whether health services are available, to produce the intended results with a minimum accessible, effective and efficient. expenditure of time and resources. Epidemiology provides data for directing public health action. The information is used when planning how to control and prevent disease in Linkages the community. To promote current and future collaboration, Through public health surveillance, a health the epidemiologists need to maintain systematically collects, analyzes, interprets and relationships with staff of other agencies and disseminates health data on an ongoing basis. institutions. Mechanisms for sustaining such linkages include official memoranda of By knowing the ongoing pattern of disease understanding, sharing of published or on-line occurrence and disease potential, a health information for public health audiences and agency can effectively and efficiently outside partners, and informal networking that investigate, prevent and control disease in the takes place at professional meetings. community. Policy Development Why is epidemiology important health education? Epidemiologists who understand a problem and the population in which it occurs are often Epidemiology is a discipline that has a crucial in a uniquely qualified position to recommend role in describing health status, identifying risk appropriate interventions. factors, and analyzing relationships between health and different hazardous agents. As a result, epidemiologists working in public health regularly provide input, testimony, and The classical epidemiological triangle of host- recommendations regarding disease control agent-environment describes how individuals strategies, reportable disease regulations, and become ill. health-care policy. What are the principles of epidemiology? How is epidemiology important to public Distribution – Epidemiology is concerned with health? the frequency and pattern of health events in a Veterinarians and others involved in the population. preventive medicine and public health Determinants – Epidemiology is also used to professions use epidemiological methods for search for causes and other factors that disease surveillance, outbreak investigation, influence the occurrence of health-related and observational studies to identify risk factors events. of zoonotic disease in both human and animal populations, Principles of Epidemiology The Primary Applications of Epidemiology Application - Epidemiology provides data for in Public Health directing public health action. An epidemiologist uses the scientific methods of descriptive and To set policy and plan programs, public health analytic epidemiology in "diagnosing" the officials must assess the health of the health of a community, but also must call upon population they serve and must determine experience and creativity when planning how to Who uses epidemiology? control and prevent disease in the community. - Researches Specified populations - Epidemiologists are - Health department official concerned with the collective health of people - The government - Health or medical practitioners uses in a community or other area and the impact of epidemiology health events on that population. This data is used to help identify priority health issues and possible causes of disease or illness What is the ultimate goal of epidemiology? The goal of epidemiology is to establish causal factors for health issues in order to improve the health and safety of entire populations Branches of Epidemiology - Cancer Epidemiology - Cardiovascular Epidemiology - Clinical Epidemiology - Environmental and Occupational Epidemiology - Epidemiologic Methods - Epidemiology of Aging - Genetic Epidemiology and Statistical Genetics The Key 6 Characteristics of Epidemiology - Design of the study - Population that has been studied - Exposure - Outcome - Covariates - Effect size Example of epidemiology Epidemiological studies measuring the risk of illness or death in an exposed population compared to that risk in an identical, unexposed population (for example, a population the same age, sex, race and social status as the exposed population).