Measures of association in epidemiological studies. Examples of measures of association include risk ratio relative risk, rate ratio, odds ratio, and proportionate mortality ratio. Measures of association are utilized to compare the. In epidemiology, an association means a correlation, often between an exposure and an outcome. For a cohort study, the odds ratio or co for disease is estimated by the measures of association 99 sample chapter from introduction to veterinary epidemiology biofolia, 2004. If youre in the baseline you have 100% of the average risk, but no extra risk. Study design epidemiology is the study of the distribution and determinants of health related states or events in specified populations, and the application of this. Epidemiologic measures of association is the property of its rightful owner. It tends to be biased towards 1 neither risk or protection at high rates of. The article also discusses in detail three kinds of risks and odd ratio. Epidemiologic measures measures of disease frequency measures of association measures of effect. Strength of association for ratio measures of association. Intervention trialscontrolled trials the first two of these designs are employed in clinical, rather than epidemiologic, studies, but often.
Measures of frequency, association and impact are the main statistical resources employed in epidemiology to describe the distribution of healthcare problems, establishing a causal relationship between exposure and disease, enabling users to evaluate the impact of preventive measures. Eric at the unc ch department of epidemiology medical center risk and rate measures in cohort studies e r i c n o t e b o o k s e r i e s cohort studies are longitudinal studies where an exposed and an unexposed group or less exposed group are followed forward in time to find the incidence of the outcome of interest e. Attributable risk is also known as excess risk which is calculated when individuals or subjects in a research are assembled on exposure status. It is the only measure of risk that can be obtained directly form a casecontrol study c. The last section describes the odds, another measure of disease frequency that is the basis for a measure of association often used in epidemiology, event definition reference natural menopause date of last menstrual period after a woman has stopped menstruating for 12 months bromberger et al. The measures of association described in the following section compare disease occurrence among one group with disease occurrence in another group. Since crosssectional studies are particularly useful for investigating chronic diseases e. Measurement of exposure and disease are covered in chapter 2 and a summary of the different types of study designs and their strengths and limitations is provided in. In a cohort study, the average of the population at the beginning and at the end of the period can be obtained for a given followup interval. Professor, department of community medicine, vmchri, madurai 2.
Epidemiology is about identifying associations between exposures and outcomes. An overview of measurements in epidemiology v3 2007. Measures of association work on multiplicative scale 44 times more likely. Measures of frequency, magnitude of association and impact. Although the terms correlation and association are often used interchangeably, correlation in a. Id like to pause for a moment to talk about correla tion and causation. These concepts apply to incidence proportions, incidence rates, and prevalence proportions, all of which are loosely called rates. Measures of association kanchanaraksa define the measures of risk used in epidemiologic studies. Measures in epidemiology young epidemiology scholars. Calculating measures of association casecontrol studies the odds ratio is the measure of association for a casecontrol study. Measures of association encompass methods designed to identify relationships between two or more variables and statistics used to measure the relationship when it exists. Calculate odds ratios in matched and unmatched casecontrol studies. Learning objectives at the end of this lecture you sh be able list the various tools used for measurement list the various measures of death list the various measures of disease 2.
A logical sequence of study designs encountered in epidemiology is. Several examples from the literature of cancer epidemiology will illustrate that the relative risk provides a stable measure of association in a wide variety of human. Eric at the unc ch department of epidemiology medical center. For now we consider that the data have been obtained in a cohort study, where the initially healthy cats are followed through a period of 5 years. Measures of association are used in various fields of research but are especially common in the areas of epidemiology and psychology, where they frequently measure of association, in statistics, any of various factors or coefficients used to quantify a relationship between two or more variables. Summarize this comparison in one measure signifying the strength of an association between an exposure and an outcome absolute or relative measures interpreting this measure definitions absolute measures difference of two measures i. Measures of frequency and association are very useful for that purpose and they are regarded as the fundamental of descriptive epidemiology. Thus, identifying the causes of disease in epidemiology inherently involves comparison between groups of people who differ by exposure. Correlation is the situation in which two or more variables, in this case exposure and. Epidemiologic measures overview epidemiologic measures are used to quantify the frequency of diseases in a population, measure the association between exposures and diseases, and address the potential impact of an. Often computed as a percentage, the par provides an estimate of the incidence of a disease in a population that is associated with or attributed to the exposure or risk factor in question, provided the association is causal 15.
Basic epidemiology starts with a definition of epidemiology, introduces the history of modern epidemiology, and provides examples of the uses and applications of epidemiology. Measures of association the measures of association refer to a wide variety of coefficients that measure the statistical strength of the relationship on the variables of interest. Epidemiologic study designs epidemiology learning materials. Latest epidemiology multiple choice questions and answers for pdf free download 1. Since the health, exposure, and demographic measures characterize population groups, inferences from associations observed in an ecological study may not. Measures of association thomas songer, phd basic epidemiology south asian cardiovascular research methodology workshop epidemiologic reasoning 1. So if you understand those, then itll be easy to understand the measures of association. Because of the result of the ratio is lower than the break even point than the exposed people are less likely to get the outcome than the unexposed. Epidemiology measures of association flashcards quizlet. Overall rate of disease in an exposed group says nothing about whether exposure is a risk factor for or causes a disease.
Let r 1 represent the rate or risk of disease in the exposed group and let r 0 represent the rate or risk of disease in the nonexposed group. 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. Since we will normally deal with i x j tables, where i and j are the number of rows and columns respectively, we need a set of basic odds ratio to show the nature and direction of the relationships. The measures of association refer to a wide variety of coefficients including bivariate correlation and regression coefficients that measure the strength and direction of the relationship between variables. Section of epidemiology and biostatistics, the university of auckland, tamaki campus, glen innes, 1142, auckland, new zealand. Differentiate between relative risks, odds ratio, and attributable risks. Cross sectional studies unc gillings school of global. The main difference between them is the units in which they. Three measures of disease occurrence are commonly used in incidence studies. Define epidemiology and recognize some of its uses interpret distribution of disease according to person, place, and time calculate measures of disease occurrence and severity define epidemiology and.
Those measures of occurrence are the building blocks of the measures of association. It indicates the likelihood of developing the disease in the exposed group relative to those who are not exposed. Measures of association effect notation and terminology. To identify any association, exposures and outcomes must first be measured. Suspicion that a factor exposure may influence occurrence of disease observations in clinical practice examination of disease patterns do subpopulations have higher or lower rates. The motivation to apply a measure such as odds lies not in the odds themselves but more in the ratio between two different odds, the odds ratio.
There were a total of 1,000 people in the study, and the study was conducted over a ten year period. How to measure the diseases, determining their causes and plan the appropriate means of controlling the diseases as well as their occurrences are very important issues address by epidemiology. These include interpreting the measures of association, and. To identify measures of association and risk as they are used in epidemiology to interpret relative risk and odds ratios and be familiar with their calculation using 2x2 tables, and to interpret the following measures of risk differences. If so, share your ppt presentation slides online with. Measures of association assume categorical or continuous level of data. It tells us how much higher the odds of exposure is among cases of a disease compared with controls. This can only be evaluated by comparing disease occurrence in an exposed group to another group that is usually not exposed. There is some overlap between these measures, and terminology is poorly standardized. Measures of association introduction we search for the determinants of health outcomes, first, by relying on descriptive epidemiology to generate hypotheses about associations between exposures and outcomes, and, second, by employing analytical epidemiology to more rigorously assess hypotheses by drawing samples of people and comparing groups to determine whether health outcomes differ based. Epidemiologic measures basic epidemiologic measures used to quantify. The relative risk rr estimates the magnitude of an association between exposure and disease. Measures of association quantify the strength and the direction of the relationship between two data sets.
Introduction to epidemiology outline purpose of epidemiology i to provide a basis for developing disease control and prevention measures for groups at risk i this translates into developing measures to prevent or control disease 619. Occasionally you might observe an incidence rate among a population that seems high and wonder whether it is actually higher than what should be expected based on, say, the incidence rates in other communities. Measures of association measures of association coursera. For acute disease studies, pr is the preferred measure of association. If you continue browsing the site, you agree to the use of cookies on this website. Ppt epidemiologic measures of association powerpoint. Epidemiology is the study of how disease is distrib uted in populations and. Comparison purpose summarize relationship between exposure and disease by comparing at least two measures of disease frequency. Common measures and statistics in epidemiological literature. An overview of measurements in epidemiology teachepi.
Here are the two most commonly used measures of association. In general, measures of disease frequency are needed to generate measures of association, and both these are needed to get measures of impact. Formulas from epidemiology kept simple 3e chapter 3. Covariance correlation both measures are used to show how closely two data sets are related to each other.
Often called the cornerstone of public health, epidemiology is the study of the distribution and determinants of diseases, health conditions, or events among populations and the application of that study to control health problems. Measures of association measures of association are utilized to compare the association between a specific exposure and health outcome, they can also be used to compare two or more populations, typically those with differing exposure or health outcome status, to identify factors with possible etiological roles in health outcome onset. All of the following are true of odds ratio except. Fundamental epidemiology terminology and measures maryland. The last section describes the odds, another measure of disease frequency that is the basis for a measure of association often used in epidemiology. If the disease is rare the odds ratio will approximate to the relative risk. Measurement, the translation of observations into a meaningful numeric form, is commonly taught in science classes with measures of length, time and mass. In a second study of 163 metropolitan areas of the united states, schroeder 9 also found an inverse association between coronary heart disease mortality rates for white males 4564 years of age and water hardness r 0. However, when you use these tables to compute measures of association there is a distinct advantage to setting them up the same way all the time. Measures in epidemiology goals and objectives of this module the goal of this module is to introduce the student to some elementary ideas of measurement in epidemiology. Control and prevention or the association for prevention teaching and research. There is no fixed convention for setting up a 2x2 also known as contingency table.
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