Smoking was later identified as a confounder, because smoking was correlated both with alcohol consumption and also with heart disease. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. An RR <1 means that the outcome is less likely to occur in the exposed group than in the unexposed group. This course illustrates the principles of public health applied to depressive disorder, including principles of epidemiology, transcultural psychiatry, health services research, and prevention. Disadvantages include a potentially high possibility of selection bias, the fact that individuals may have difficulty recalling certain exposures (termed recall bias), and the requirement for the existence of medical and/or exposure records. Observation bias arises from systematic differences in the method of obtaining information from subjects/cases. The horizontal axis represents the date when an individual became ill, also called the date of onset. Stages of Disease B. Mechanisms and Causes of Disease C. Host, Agent, Environment, and Vector D. Risk Factors and Preventable Causes 1. The first step in an analytic study is to form some conjecture regarding observed exposures and health outcomes. These are updated as new data come in and thus are subject to change. In scientific studies, the most common P value is .05, which means an error of <5% of detecting an association between a variable and an outcome is acceptable. Although these steps are accomplished in a systematic fashion, they frequently overlap or occur concurrently. Epidemiology according to the science of public health. However, there are methods to interpret test results to reduce their inherent fallibility. Tabulate the frequency of clinical signs, symptoms, and laboratory findings among children with chickenpox in Cincinnati, Ohio. Type II error, also known as a false negative, is when the null hypothesis is accepted when it actually should have been rejected. Therefore, the accuracy of a test is a trade-off between each of these parameters. The resulting rate allows epidemiologists to compare disease occurrence across different populations. This lesson is intended to answer those questions by describing what epidemiology is, how it has evolved and how it is used today, and what some of the key methods and concepts are. The odds ratio (OR) represents the odds that an outcome will occur from a particular exposure, compared with the odds of the outcome occurring in the absence of that exposure. In other words, there is an important characteristic of the controls that make them different from the general population. You will be subject to the destination website's privacy policy when you follow the link. The overall shape of the epi curve can give clues to the type of exposure that resulted in the outbreak. In other words, the clinician’s “patient” is the individual; the epidemiologist’s “patient” is the community. Disease surveillance is a necessary public health role. False-positive test results do not affect the NPV. Why would it be important to find the right cause of the disease? What are the financial benefits of addressing this issue at the population level as opposed to the individual level? Screening tests tend to have higher sensitivity and lower specificity, because the purpose of such a test is to detect the maximum number of individuals with the particular disease condition. In this case, the data are “pulled” by the requestor, usually during emerging diseases or significant changes in disease incidence. In this example, the multiplier would be 100, and the incidence rate would be 12.7 cases per quarter per 100 students (or 12.7%). In yet other cases, an inverse relationship is observed when greater exposure of a protective factor leads to lower incidence of outcomes. An example of the former was a spurious conclusion drawn from a study of the relationship between alcohol consumption and heart disease. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures. When the study ended, productivity went back to prestudy levels. Several sets of systematic criteria for determining causality have been proposed: 1) Strength—Although a small association does not mean that there is not a causal effect, the larger the association, the more likely that it is causal. Analytical epidemiology is accomplished through either observational studies or interventional studies. This course covers basic epidemiology principles, concepts, and procedures. Retrospective cohort studies have several advantages over prospective cohort studies. Observational studies – we do not interfere in the process of the disease, but simply observe the disease and the associated factors. First, in a single-blinded design, the participants are unaware whether they are in the study group or the control group. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. In the former, the investigator does not control the exposure between the groups under study and typically cannot randomly assign subjects to study groups. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. The epidemic (epi) curve shows progression of an outbreak over time. 4th ed. To calculate the sensitivity and specificity of a test, consider the following 2 × 2 table (see Table: Calculating Test Sensitivity and Specificity). The group has no size limitation but must be able to be defined. Distribution implies that diseases and other health outcomes do not occur randomly in populations; determinants are any factors that cause a change in a health condition or other defined characteristic; morbidity is illness due to a specific disease or health condition; mortality is death due to a specific disease or health condition; and the population at risk can be people, animals, or plants. How are they both important to public health? Principles of epidemiology Consider ethical issues related to respect for persons, beneficence, and justice as described in “The Belmont Report.” Topic 8: Environment and Genetics. In epidemiology, variables are either associated or they are not. Last JM, editor. Rates are typically expressed as a measure of the frequency with which an event occurs in a defined population in a defined time (eg, the number of foodborne Salmonella infections per 100,000 people annually in the USA). For instance, animal rabies is endemic in the USA. Incidence rates are usually expressed by a multiplier that makes the number easier to conceptualize and compare. Place criteria usually include a geographic boundary such as a state or local area, a school class, or a particular restaurant. II. What is important about your disease? Frequency includes not only the number of such events in a population, but also the Identify risk factors for developing diseases 5. The interdependence of epidemiological studies and their essential unit within a theoretical, technical, and ethical framework is an important theme of this book. , DVM, MPH, DACVPM, Lincoln Memorial University; , DVM, MPVM, DACVPM, Department of Pathobiology, College of Veterinary Medicine, Auburn University. Epidemiology is a discipline that studies the distribution and determinants of disease. Common terms and phrases. Think about how principles of epidemiology are being applied—or could be applied—to address the problem. There are two broad types of epidemiological studies: 1. Case series are listings of a larger number of cases, usually presented consecutively (eg, a characterization of dog bite incidents in a population of veterinarians and/or technicians over time). The results of interventional studies can be very powerful in proving causality or identifying efficacy of various interventions. Obviously, each member of the cohort must not have the disease or outcome at the beginning of the study. The major advantage of the prospective cohort study is that many different exposures can be considered and analyzed for influencing the outcome under study. Count health-related events 2. The applications of epidemiology are diverse and include identifying causal mechanisms of disease, diagnostic testing, determining prognosis, and testing new treatments. A concept is an idea, but the word is usually reserved for complex, or interrelated, ideas. Preventing disease and promoting health. ECOLOGICAL ISSUES IN EPIDEMIOLOGY A. What is important about your exposure? Recall bias: Cases and controls may remember an exposure differently (and non-randomly). When analyzing results of an epidemiologic study, there are two categorical types of error when either accepting or rejecting the null hypothesis. • Epidemiology is the basic science of Preventive and Social Medicine. Confounding: In epidemiologic studies, a confounder is a variable that is not considered in the study design but is associated with the exposure and exerts an effect on the outcome. If you continue browsing the site, you agree to the use of cookies on this website. verify here. Time parameters may be after an implicated meal (if foodborne) or other types of exposures. An epidemiological profile helps to coordinate activities and policies from various agencies and organizations to improve health. The link you have selected will take you to a third-party website. Descriptive methods are commonly applied to little-known diseases; they use preexisting data, address the questions of who/where/when, and identify potential associations for more in-depth analytical studies. The practice diagnosed 542 clinical cases in a particular year, 83 of which died from the disease in the course of that year. In a propagated source outbreak, the peaks of cases occur one incubation period apart. Graph the number of cases of congenital syphilis by year for the country, ____ 5. Although knowledge of the complete natural history is not absolutely necessary for treatment and control of disease in a population, it does facilitate the most effective interventions. In animals, time may refer to milking shift, breeding season, lambing/calving season, at weaning, during shipment, on arrival at the feedlot, dry vs wet season, etc. Introduction to Epidemiology 3. It is predicted that by 2020 depressive disorder will be the most important cause of disease burden in the entire world! 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. Another attribute of an outbreak that can be illustrated by the epi curve is the period of incubation. Principles of Epidemiology Workbook: Exercises and Activities Ray M. Merrill Limited preview - 2011. 3. Please confirm that you are a health care professional. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied. The following steps in investigating disease outbreaks are used by the CDC: prepare for field work, confirm the existence of an outbreak, verify the diagnosis, establish a working case definition, engage in systematic case finding, apply descriptive epidemiology, develop and test hypotheses (analytical epidemiology), implement control measures, and communicate findings. Students of journalism are taught that a good news story, whether it be about a bank robbery, dramatic rescue, or presidential candidate’s speech, must include the 5 W’s: what, who, where, when and why (sometimes cited as why/how). Principles of Epidemiology when applied to the population health problem of obesity. Confounders can either produce a false association between variables or mask a true association between variables. Principles of Epidemiology. For diseases of high prevalence, the PPV of a test will be high and the NPV will be low. 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