Epidemiology is a population science that underpins health improvement and health care, by exploring and establishing the pattern, frequency, trends, and causes of a disease. Key terms in this definition reflect some of the important principles of epidemiology. The proportion of female dogs among those found to have parasite infections would be 643/(889 + 643), or 0.42. The methodology is very similar to that of the prospective cohort study, except that all the events (exposures and outcomes) have already occurred; the investigator is merely looking back rather than forward. Therefore, if a test was reported to have an NPV of 100%, the validity of a positive test result is still unknown. This course covers basic epidemiology principles, concepts, and procedures useful in the surveillance and investigation of health-related states or events. When a particular disease is observed relative to the variables of person, place, and time, it is often systematically described to facilitate more in-depth study. Morbidity is the measure of illness in a population, and numbers and rates are calculated in a similar fashion as with incidence and prevalence. Compare frequency of brain cancer among anatomists with frequency in general population, ____ 3. Focused studies can help assist epidemiologists to determine why those differences have occurred and to identify specific risk factors. In the latter case, cause-specific mortality is expressed as the case fatality rate (CFR), which is the number of deaths due to a particular disease occurring among individuals afflicted with that disease in a given time period. That is why some investigators “match” cases and controls. 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). Epidemiology is applied in many areas of public health practice. Select interventions for prevention and control 9. Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Place variables commonly illustrate geographic differences in the occurrence of a particular disease. The 5 W’s are the essential components of a news story because if any of the five are missing, the story is incomplete. Public health surveillance is defined as the ongoing systematic collection, analysis, interpretation, and dissemination of outcome-specific data essential to the planning, implementation, and evaluation of public health practice. Key Takeaways Key Points. The former is more subjective than the latter but can be just as effective, especially in field epidemiologic conditions. Introduction to Epidemiology 3. Epidemiology is based on two fundamental assumptions. In summary, descriptive epidemiology serves to describe the occurrence of disease in a population. Therefore, if the study groups are comprised of differing fractions of employed and unemployed people, the results may very well be skewed. 1. They assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, or other so-called potential risk factors. 4th ed. ORs are calculated using a 2 × 2 frequency table ({blank} Calculating an Odds Ratio. 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. Epidemiology is the study of the patterns, causes, and effects of health and disease conditions in defined populations. The positive predictive value (PPV) of a test is the probability of a patient actually having the disease condition when the test is positive. We handle assignments in a multiplicity of subject areas including Admission Essays, General Essays, Case Studies, Coursework, Dissertations, Editing, Research Papers, and Research proposals. 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. Typical epi curves from common sources include 1) a common specific point source in which all cases were exposed at the same time and place (eg, a foodborne illness outbreak); 2) a common source with continuous exposure in which although the source is common, cases gradually rise before either peaking or plateauing and declining; and 3) a common source with intermittent exposure in which the peaks occur at irregular times corresponding to the earlier exposures. Principles Of Epidemiology. 2. Cates W. Epidemiology: Applying principles to clinical practice. Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. The answer is no, because of the difference between average and median. Although it did not prove causality alone, it was instrumental in the U.S. Public health officials investigate disease outbreaks to control them, to prevent additional illnesses, and to learn how to prevent similar outbreaks from happening in the future. Therefore, if the PPV of a test is 100%, the validity of a negative test result is still unknown. Person: Who is affected by this disease? In other words, there is an important characteristic of the controls that make them different from the general population. 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. 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. Establish priorities for allocating resources 8. Identify causes or determinants of disease 6. The most common measurement of association in case-control studies is the odds ratio. Epidemiology is concerned with the frequency and pattern of health events in a population: Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population. Last JM, editor. Describe clinical patterns 4. 10987654321 Typeset in 10\12 Minion by Newgen Imaging Systems (P) Ltd, Chennai, India. NIH. PUB 540 Principles of epidemiology Topic 2 DQ 1. pub 540 Principles of epidemiology Topic 2 DQ 1. Epidemiology is a discipline that studies the distribution and determinants of disease. Researchers began the study in 1948 by recruiting 5,209 men and women, 30–62 yr old, from the town of Framingham, Massachusetts. Explain the biological and genetic factors that affects a population’s health. Another attribute of an outbreak that can be illustrated by the epi curve is the period of incubation. In this type of study, a group of individuals (termed a cohort) is observed over time for changes in health outcomes. verify here. This course is designed for federal, state, and local government health professionals and private sector health professionals who are responsible for disease surveillance or investigation. What is important about your disease? Those tests or diagnostic procedures known to produce the absolute best results are termed “gold standard” tests. In medical research, these exposures typically include interventions such as vaccines, therapeutic drugs, surgical techniques, or medical devices. They are relatively quick, easy, and inexpensive. Consider a study comparing library usage between students at two universities. Think about how principles of epidemiology are being applied—or could be applied—to address the problem. 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. Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site, ____ 4. For diseases of high prevalence, the PPV of a test will be high and the NPV will be low. For example, in a class of veterinary students in which 88 are female and 14 are male, the sex ratio of female students to male students is 88/14, or 6.3 to 1. Principles of Epidemiology Workbook: Exercises and Activities Ray M. Merrill Limited preview - 2011. Usually, cases remember exposures more clearly than controls. In addition to outbreaks having common sources, they can have propagated sources, in which cases can directly infect other cases separate from the initial source. An example is the healthy worker effect, which refers to the phenomenon that employed groups have lower mortality than the general population. A subset of an epidemic is an outbreak, when the higher disease occurrence occurs in a smaller geographic area and shorter period of time. What is important about your disease? However, there are methods to interpret test results to reduce their inherent fallibility. What is important about your exposure? In epidemiology, health surveillance is accomplished in either passive or active systems. Since that time, they have accomplished extensive serial physical examinations and surveys relating to the development of cardiovascular disease. 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. Time variables are important to describe when disease occurs in relation to various factors of potential exposure and vulnerability. In this type of study, subjects are selected as either having a particular outcome (cases) or not having the outcome (controls). Sensitivity and specificity are inversely proportional, ie, when one increases, the other decreases. It is designed for federal, state, and local government health professionals and private sector health professionals who are responsible for disease surveillance or investigation. ISBN 9780199543144, 417 … Although the communities may be selected at random, the individuals within them obviously are not. 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. When the study ended, productivity went back to prestudy levels. (prevention, control and treatment). An example of the former was a spurious conclusion drawn from a study of the relationship between alcohol consumption and heart disease. Disadvantages include the high cost in terms of money and time during the period of the study and the inability to study very rare diseases or health outcomes unless the cohort is extremely large. When the period of the study is from the present into the future, the study is a prospective cohort study. Learning Objectives . This concept seems simple at first, but misinterpretations can lead to erroneous study results and conclusions. If the variables are not associated, there is no relationship; they are independent. For animal populations, “place” may refer to housing (eg, indoors vs outdoors, pen number or stall) or type of herd management (eg, intensive feedlot confinement vs extensive grazing). A major advantage of randomized controlled clinical trials is an inherently high validity for identifying differences in therapeutic efficacy of various interventions. Although the risk in an epidemiological investigation is usually minimal, most people who take part gain no personal benefit. Observation bias arises from systematic differences in the method of obtaining information from subjects/cases. To make the proper diagnosis and prescribe appropriate treatment for a patient, the clinician combines medical (scientific) knowledge with experience, clinical judgment, and understanding of the patient. The definition of epidemiology is “the study of disease in populations and of factors that determine its occurrence over time.” The purpose is to describe and identify opportunities for intervention. When two variables are associated, it is sometimes obvious as to whether it is causal. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.(2). Passive surveillance occurs when individual health care providers or diagnostic laboratories send periodic reports to the public health agency. Applications of epidemiology in public health 1. The same is true in characterizing epidemiologic events, whether it be an outbreak of norovirus among cruise ship passengers or the use of mammograms to detect early breast cancer. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among persons with … It emphasizes theories and principles, as the bedrock of methodology, countering the mounting criticism that epidemiology is an atheoretical discipline. We can help. The natural history begins before infection (prepathogenesis period) when the agent simply exists in the environment, includes the factors that affect its incidence and distribution, and concludes with either its disappearance or persistence (endemnicity) in that environment. This book, then, aims to explain the ideas underlying the language, principles, and basic methods in epidemiology. In another example, consider a large veterinary practice in the southwest USA that frequently sees dogs with coccidioidomycosis. Therefore, studies are designed in ways that minimize the sources and effects of bias. Note that this assumption of no association is made even though the epidemiologist often thinks that some association actually exists. Although the risk in an epidemiological investigation is usually minimal, most people who take part gain no personal benefit. Count health-related events 2. The more specific the association between an exposure and an outcome, the higher the probability of causation. Epidemiology is the study of the factors that determine the occurrence and distribution of diseases in populations. Additionally, this type of study is not usually applicable for discovering disease etiologies; observational studies are much better suited for this purpose. Finally, if an association exists (positive or negative), it is either causal or noncausal related to the outcome. ECOLOGICAL ISSUES IN EPIDEMIOLOGY A. A disease is considered endemic when it is constantly present within a given geographic area. Preventing disease and promoting 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. The negative predictive value (NPV) is the probability of a patient not having the disease condition when the test is negative. principles, and methods of epidemiology / by Raj S. Bhopal. Type II error, also known as a false negative, is when the null hypothesis is accepted when it actually should have been rejected. Printed in Great Britain on acid-free paper by Biddles Ltd, Guildford … The numerator and denominator may be independent of each other. • Applying epidemiological principles and methods to problems encountered in the practice of medicine has led to the development of- “Clinical Epidemiology” 20. Specificity, in contrast, is the probability of a negative test result in the absence of disease, thereby correctly classifying an individual as disease-free (regarding that particular condition). These studies are commonly undertaken to assess the quality and effectiveness of educational programs, behavioral changes, or mass interventions such as water fluoridation. Epidemiology is concerned with the distribution and determinants of health and disease, morbidity, injury, disability, and mortality in populations. The legacy of this great resource continues as the Merck Veterinary Manual in the US and Canada and the MSD Manual outside of North America. Epidemiology according to the science of public health. Concepts of Epidemiology: Integrating the Ideas, Theories, Principles and Methods of Epidemiology , 2nd edn. Common place variables include comparisons across national, state, and municipal boundaries and between urban and rural communities. In yet other cases, an inverse relationship is observed when greater exposure of a protective factor leads to lower incidence of outcomes. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The investigators jump back in time to identify a cohort of individuals at a point in time before they developed the outcomes of interest, and try to establish their exposure status at that point in time. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. Resources . This course is designed for federal, state, and local government health professionals and private sector health professionals who are responsible for disease surveillance or investigation. An attack rate is an incidence rate; however, the period of susceptibility is very short (usually confined to a single outbreak). Finally, a pandemic occurs when an epidemic becomes global in scope (eg, influenza, HIV/AIDS). Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events. In epidemiology, the patient is the community and individuals are viewed collectively. Recall bias: Cases and controls may remember an exposure differently (and non-randomly). Selection bias results from the identification of subjects/cases from a subset that is not representative of the entire population at risk. Case-control studies have several advantages. Community health assessment (Community Diagnosis) and priority setting. The practice diagnosed 542 clinical cases in a particular year, 83 of which died from the disease in the course of that year. Confounders can either produce a false association between variables or mask a true association between variables. When corrected for the effects of this confounder, no association was found between alcohol consumption and heart disease. An incidence rate takes the population at risk into account. If you continue browsing the site, you agree to the use of cookies on this website. Two essential components are the number of new cases and the period of time in which those new cases appear. Passive surveillance is useful for longterm trend analysis (if reporting criteria remain consistent) and is much less expensive than active surveillance. In fact, epidemiology is often described as the basic science of public health, and for good reason. Solution of Public Health Problems and … Conversely, an RR >1 means the outcome is more likely to occur in the exposed group than in the unexposed group. Place criteria usually include a geographic boundary such as a state or local area, a school class, or a particular restaurant. PRINCIPLES OF EPIDEMIOLOGY Epidemiology in Public Health Recently, a news story described an inner-city neighborhood’s concern about the rise in the number of children with asthma. PREREQUISITES None. The word epidemiology is derived from the Greek words, epi means among, demos mean people and logos mean study. Given the high specificity of confirmatory tests, a positive result strongly implies that disease is present. Known as ecologic fallacy, it is described by “associations observed at the group level do not necessarily hold true at the individual level.” As an example, one could determine that the average IQ of a class of veterinary students is above average (which, by definition, would be 100). The Merck Veterinary Manual was first published in 1955 as a service to the community. PPV and NPV are clinically relevant, because they are directly related to the prevalence of disease. Principles of Epidemiology Workbook: Exercises and Activities Ray M. Merrill Limited preview - 2011. For example, when a patient with diarrheal disease presents, both are interested in establishing the correct diagnosis. In the study, it was concluded that alcohol consumption was significantly associated with heart disease. It is against these gold standards that newer, usually faster and more convenient, tests are measured in terms of sensitivity and specificity. In other words, this is the error of accepting an alternative hypothesis (the real hypothesis of interest) when the results can actually be attributed to chance. Epidemiology. History of Epidemiology. Ecologic studies also have several disadvantages. This bias can be alleviated in one of two ways. What has the literature said about the exposure-disease relationship? 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. We do not control or have responsibility for the content of any third-party site. How are they both important to public health? Common person variables include age, sex, race, socioeconomic status, marital status, religion, smoker/nonsmoker, etc. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences. To calculate the sensitivity and specificity of a test, consider the following 2 × 2 table (see Table: Calculating Test Sensitivity and Specificity). Many definitions have been proposed, but the following definition captures the underlying principles and public health spirit of 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 (1). If the variables are associated, that relationship can be either positive or negative. epidemiology is an atheoretical discipline. Dictionary of epidemiology. Additionally, their application is limited to the study of one outcome. For example, in a common point source outbreak, the investigation frequently identifies the event (eg, meal, social gathering, etc) when the exposure occurred. These systematic descriptions commonly take the form of case reports, case series, or cross-sectional studies. Additionally, they can address rare outcomes, because the cases are selected after having already developed the disease or outcome. NPV is calculated as true negatives divided by the sum of the true negatives and the false negatives: d/(c + d). In a propagated source outbreak, the peaks of cases occur one incubation period apart. Although these steps are accomplished in a systematic fashion, they frequently overlap or occur concurrently. In a propagated source outbreak, person-to-person transmission occurs, often through several cycles before declining. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. The horizontal axis represents the date when an individual became ill, also called the date of onset.
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