Epidemiology Lecture Notes PDF

29/11/2024 EPIDEMIOLOGY 1 EPIDEMIOLOGY Epi: On or Upon Demos: People Logos: the Study of “The study of what befalls a population” 2 1 ...

29/11/2024 EPIDEMIOLOGY 1 EPIDEMIOLOGY Epi: On or Upon Demos: People Logos: the Study of “The study of what befalls a population” 2 1  29/11/2024 EPIDEMIOLOGY “Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems” 3 EPIDEMIOLOGY Study Scientific discipline with sound methods of scientific inquiry at its foundation. Data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, differs from what might be expected. It also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences. Epidemiology is often described as the basic science of public health (quantitative discipline, method of causal reasoning) But it is not just a research activity but an integral component of public health. 4 2  29/11/2024 EPIDEMIOLOGY Distribution It is concerned with the frequency (rate) and pattern (time, place and person) of health events in a population. Characterizing health events by time, place, and person are also activities of descriptive epidemiology. 5 EPIDEMIOLOGY Determinants Epidemiology is also used to search for determinants, which are the causes and other factors that influence the occurrence of disease and other health-related events. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events Ideally, the findings provide enough evidence to direct prompt and effective public health control and prevention measures. 6 3  29/11/2024 EPIDEMIOLOGY Health - related states or events Epidemiology was originally focused exclusively on epidemics of communicable diseases but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. Middle of 20th century: chronic diseases, injuries, birth defects, maternal- child health, occupational health and environmental health. Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. 7 EPIDEMIOLOGY Specified populations Although epidemiologists and direct health- care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.” The clinician is concerned about the health of an individual; the epidemiologist is concerned about the collective health of the people in a community or population. 8 4  29/11/2024 EPIDEMIOLOGY Application Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. 9 EPIDEMIOLOGY- HISTORY 10 5  29/11/2024 EPIDEMIOLOGY - HISTORY Hippocrates (400 B.C) Disease occurrence from a rational rather than a supernatural viewpoint. “On Airs, Waters, and Places” suggested that environmental and host factors such as behaviors might influence the development of disease. 11 EPIDEMIOLOGY - HISTORY John Graunt (1662) - Haberdasher Published a landmark analysis of mortality data in 1662. First publication which quantified patterns of birth, death, and disease occurrence, noting disparities between males and females, high infant mortality, urban/rural differences, and seasonal variations. 12 6  29/11/2024 EPIDEMIOLOGY - HISTORY John Snow (1854) “Father of field epidemiology.” Twenty years before the development of the microscope, he conducted studies of cholera outbreaks both to discover the cause of disease and to prevent its recurrence. His work illustrates the classic sequence from descriptive epidemiology to hypothesis generation to hypothesis testing (analytic epidemiology) to application. 13 EPIDEMIOLOGY - HISTORY 14 7  29/11/2024 EPIDEMIOLOGY - HISTORY Mid- and late-1800s: epidemiological methods began to be applied in the investigation of disease occurrence. Most investigators focused on acute infectious diseases. In the 1930s and 1940s, epidemiologists extended their methods to noninfectious diseases. In the 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 roots. New infectious agents, changed agents, deliberate spread agents. Today, public health workers throughout the world accept and use epidemiology regularly to characterize the health of their communities and to solve day-to-day problems, large and small. 15 EPIDEMIOLOGY - USES 1. Assessing the community’s health: Public health officials responsible for policy development, implementation, and evaluation use epidemiologic information as a factual framework for decision making. 2. Making individual decisions: Many individuals may not realize that they use epidemiologic information to make daily decisions affecting their health 3. Completing the clinical picture When investigating a disease outbreak, epidemiologists rely on health-care providers and laboratories to establish the proper diagnosis of individual patients. But epidemiologists also contribute to physicians’ understanding of the clinical picture and natural history of disease (eosinophilia-myalgia syndrome). 4. Searching for causes Much epidemiologic research is devoted to searching for causal factors that influence one’s risk of disease. Ideally, the goal is to identify a cause so that appropriate public health action might be taken. 16 8  29/11/2024 EPIDEMIOLOGY IN DENTISTRY - AIMS 1. Describing normal biologic processes (tooth eruption) 2. Understanding the natural history of diseases. 3. Revealing the distribution of disease. 4. Identifying the determinants of disease. 5. Testing hypotheses for disease prevention and control (Fluoride – caries). 6. Planning and evaluating health care services. Describe: - Distribution of disease (treated & untreated) - Population’s utilization of healthcare services - Availability and productivity of health care services help decisions on services and types of personel required 17 EPIDEMIOLOGY - APPROACH Counts cases or health events, and describes them in terms of time, place, and person Divides the number of cases by an appropriate denominator to calculate rates Compares these rates over time or for different groups of people. 18 9  29/11/2024 EPIDEMIOLOGY - APPROACH WHAT IS AN EPIDEMIOLOGICAL STUDY? It is a scientific process of answering a question using data from a population. 19 EPIDEMIOLOGY - RESEARCH STAGES OF AN EPIDEMIOLOGICAL STUDY 1. Observation of the epidemiological phenomenon 2. Search of the existing bibliography on the matter 3. Elaboration of the theoretical framework: hypothesis and objectives 4. Study design: o Subjects under study (Target population, accessible, under study) o Variables (characteristics that must be measured: age, sex, school level, etc.) o Measuring instruments: (questionnaires / observation) 5. Conducting the study (field work) 6. Storage and processing of data 7. Analysis of the data obtained 8. Formulation of the conclusions report and its publication 20 10  29/11/2024 EPIDEMIOLOGY - RESEARCH RESEARCH PROJECT – STEPS 1. Preliminary steps: Formulate research question and aims Study design 2. Planification 3. Fieldwork 4. Analysis of the results 21 EPIDEMIOLOGY - RESEARCH The motivation in every research project is the observation of an epidemiologic phenomenon in our dental practice or research activity. Once we know What to study the next step is bibliographic research which allows us to understand the current knowledge. 22 11  29/11/2024 EPIDEMIOLOGY DEFINE YOUR RESEARCH QUESTION Spend enough time to develop a good question READ, READ, READ A thorough literature review will help identify a high-quality question Look for knowledge gaps or areas of controversy Are you interested/excited/convinced about your idea? “The first principle is that you must not fool yourself, and you’re the easiest person to fool.” (Richard Feynman) 23 EPIDEMIOLOGY - RESEARCH WHAT MAKES A GOOD RESEARCH QUESTION? 1. Be specific 2. Address an important and relevant issue 3. Be novel 4. Be practical 5. Be within a reasonable scope 24 12  29/11/2024 EPIDEMIOLOGY - RESEARCH We have identified the problem Know the state of the art Determined the problem justification Constructed a theoretical frame Write Research Hypotheses and Specific Aims 25 EPIDEMIOLOGY - RESEARCH A hypothesis is a tentative statement that proposes a possible explanation to some phenomenon or event. SOLID HYPOTHESIS Predicts relationships between variables (cause and effect) Address at least a part of the research question It is well-grounded in existing literature and knowledge 26 13  29/11/2024 EPIDEMIOLOGY - RESEARCH GOOD QUALITY HYPOTHESIS It makes a prediction. It describes the relationship between an independent (controlled) variable and a dependent (measured outcome) variable. It is feasible for the scope of your project 27 EPIDEMIOLOGY - RESEARCH THE AIMS SHOULD: Reflect the purpose of the study Be clear and be expressed in a realistic way Be measurable 28 14  29/11/2024 EPIDEMIOLOGY - RESEARCH DEVELOP SPECIFIC AIMS Infinitive Begin with the end in mind The specific aim or aims should be directly linked to the hypothesis. Each aim should be highly focused FEASIBILITY (time, resources, statistical power) 29 EPIDEMIOLOGY - RESEARCH Key words 1. Include your techniques and/or specific methodology 2. Focus on the main topic of your research 3. Avoid keywords that are only one word 4. Avoid overlapping keywords in your title and those in your keyword list. 5. Follow the journal guidelines when selecting keywords (U.S. National Library of Medicine’s collection of Medical Subject Headings (MeSH) 6. Perform keyword research before submitting your article. 30 15  29/11/2024 EPIDEMIOLOGY - RESEARCH PRINCIPLES OF RESEARCH ETHICS 1. Obtain informed consent from potential research participants 2. Minimize the risk of harm to participants 3. Protect their anonymity and confidentiality 4. Avoid using deceptive practices 5. Give participants the right to withdraw from your research. 31 EPIDEMIOLOGY - RESEARCH RESEARCH PROJECT – STEPS 1. Preliminary steps: Formulate research question and aims Study design 2. Planification 3. Fieldwork 4. Analysis of the results 32 16  29/11/2024 EPIDEMIOLOGY - RESEARCH We must choose the type of epidemiological study that will answer our research question. It will depend on: Research aims Association between risk factor and illness Illness characteristics Time and resources available (Nielsen, 2017) 33 EPIDEMIOLOGY - RESEARCH NON-EXPERIMENTAL STUDIES The variables are not manipulated but simply observed to detect how the outcome is affected (observational) They attempt to assess the relationship between exposures and disease by observing exposure- disease associations as they naturally occur in the population under study. 34 17  29/11/2024 THE CROSS-SECTIONAL STUDY 35 NON-EXPERIMENTAL STUDIES THE CROSS-SECTIONAL STUDY Both exposure to risk factors and the health outcomes in a group of people who are, or are assumed to be, a sample of a particular population (a “cross section”) are assessed at the same time (analytic). Measure health information at a given point of time (snapshot) Prevalence study (proportion of a particular population found to be affected by a medical condition at a specific point in time). The population selected should represent the whole population. 36 18  29/11/2024 NON-EXPERIMENTAL STUDIES THE CROSS-SECTIONAL STUDY Advantages: Inexpensive and easy to conduct Provide information about exposures and outcomes Good way of assessing the health needs of a population (Planification of health services) Several affections can be analyzed at the same time The first step for prospective studies Limitations: The information is collected at a single point in time. It cannot be used to determine if a particular exposure caused the disease or not. Not useful for rare diseases or acute illnesses Don’t determine the incidence Don’t define the temporal sequence of the disease 37 THE COHORT STUDY 38 19  29/11/2024 NON-EXPERIMENTAL STUDIES THE COHORT STUDY A cohort study samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation). The researcher records whether each study participant is exposed or not to a risk factor and tracks the participants to see if they develop the disease of interest. After a period of time, the investigator compares the disease rate in the exposed group with the disease rate in the unexposed group. If the disease rate is substantively different in the exposed group compared to the unexposed group, the exposure is said to be associated with illness. 39 NON-EXPERIMENTAL STUDIES Relative Risk (RR): A ratio of the probability of the event (outcome variable) occurring in the exposed (risk factor) group to the probability of the outcome occurring in a non-exposed (no-risk factor) group. RR > 1 exposure is associated with an Incidence rate in exposed group increased risk of disease RR = RR = 1 The risk is the same Incidence rate in unexposed group RR < 1 The risk is lower 40 20  29/11/2024 NON-EXPERIMENTAL STUDIES THE COHORT STUDY Advantages: 1. Time sequence of events can be determined (useful when trying to determine what caused the disease – causality) 2. RR and incidence rates can be calculated. 3. Information about several different outcomes/risk factors can be collected at the same time (sub- analyses) 4. Good for rare exposures Limitations: 1. High costs (large number of people being followed over a long period of time) 2. Changes in diagnostic methods and criteria with time. 3. Not good for rare diseases Challenges Ensuring the people who started the study stay until the end (this will affect the results of the study) 41 THE CASE CONTROL STUDY 42 21  29/11/2024 NON-EXPERIMENTAL STUDIES CASE CONTROL STUDY Study of persons with the disease (or another outcome variable) of interest and a suitable control group of persons without the disease (comparison group, reference group). The potential relationship of a suspected risk factor or an attribute to the disease is examined by comparing the diseased and non-diseased subjects with regard to how frequently the factor or attribute is present (or, if quantitative, the levels of the attribute) in each of the groups (diseased and nondiseased). 43 NON-EXPERIMENTAL STUDIES Odds ratio (OR): The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. OR=1 Exposure does not affect odds of outcome OR>1 Exposure associated with higher odds of outcome OR