Mobile Navigation. Prevention Research Center in St. Washington University in St. Louis, MO prcstl wustl. Saint Louis University. Louis, MO Orlando, FL: Academic Press; A framework for evaluation of secondary data sources for epidemiological research. Int J Epidemiol ; Stallones RA. Epidemiology and public policy: pro- and anti-biotic. Current issues and challenges in chronic disease control. Taubes G. Epidemiology faces its limits.
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Terris M. The epidemiologic tradition. The Wade Hampton Frost Lecture. Epidemiology as a guide to health policy. The complex tasks of the second epidemiologic revolution: the Joseph W. Mountin Lecture. J Public Health Policy ; Public health surveillance in the United States.
Applied Epidemiology: Theory to Practice, 2nd Edition
Public Health Rep ; Assessing prevention effectiveness using data to drive program decisions. Public health surveillance for chronic conditions: a scientific basis for decisions. Stat Med ; University of California San Francisco. US Dept of Energy.
Office of Environment, Safety and Health. Comprehensive epidemiologic data resource. US Public Health Service. Smoking and Health. Healthy People. Epidemiologists in the United States: an assessment of the current supply and the anticipated need. Am J Prev Med ; Biostatistics and epidemiology programs in schools of public health. In: Work TH, ed.
NIH ; World Health Organization. Geneva: WHO; Tobacco smoking as a possible etiological factor in bronchogenic carcinoma: a study of proved cases. Wynder EL. Applied epidemiology. Workshop on guidelines to the epidemiology of weak associations. Prev Med ; One is to determine the magnitude and impact of diseases or other conditions in populations or in certain segments of populations. This information can help to set priorities for investigation and control, to decide which subgroups of the population should be the focus of investigation, and to determine what types of treatment facilities are needed.
Epidemiologic studies can also be used to ascertain the natural history, clinical course, and pathogenesis of disease. They can be used to evaluate disease prevention programs and preventive and therapeutic interventions. Most often, epidemiology is used to learn about the etiology of disease. This chapter addresses methodologic concepts and issues that are most pertinent to epidemiology as it is used in public health settings and health care organizations. The intent is to give the reader an overview of key topics. The chapter assumes knowledge of the basics of epidemiology—the calculation of incidence and prevalence and the estimation of measures of association relative risk and odds ratios.
It does not cover statistical analysis of epidemiologic data or the mechanics of estimating sample size and statistical power. Instead it focuses on these concepts as they affect the design and interpretation of epidemiologic studies. Some of the material is adapted from other sources Friedman ; Kelsey et al. Study Designs Epidemiologic studies can be broadly categorized as either observational or experimental.
In observational studies, relationships are studied as they occur 35 36 Applied Epidemiology in nature.
Ross C. Brownson and Diana B. Petitti
In experimental studies, the investigator intervenes and studies the effects of the intervention. Observational studies have two fundamental objectives—to describe the occurrence of disease or disease-related phenomena and to explain them. Studies attempting to identify the causes of disease are generally called analytic epidemiologic studies. Analytic studies address the question of why diseases are distributed the way they are.
Most analytic epidemiologic studies are observational; that is, the investigator observes what is occurring in the study populations of interest and does not interfere with what he or she observes. Case-control, cohort, experimental, and some hybrid study designs are discussed in this chapter as analytic study designs. The distinction between descriptive and analytic studies is not, however, clear-cut Friedman Thus, a descriptive study may provide data that give a clear answer to a specific question.
Cross-sectional study designs are regularly used both descriptively and analytically. The distinction between description and analysis is frequently blurred in cross-sectional studies. Cross-sectional studies have a particularly important role in planning and evaluating public health programs.nttsystem.xsrv.jp/libraries/88/sita-kostenlose-handyspiele.php
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For this reasons, cross-sectional studies are discussed in detail in a separate section. Descriptive Studies Descriptive studies provide information on the frequency of occurrence of a particular condition and on patterns of occurrence according to such attributes as person, place, and time. Routinely collected statistics from such sources as mortality data, hospital discharge records, general health surveys, and disease surveillance programs are used for most descriptive studies see Chapter 4. Characteristics related to "person" often include age, gender, race, ethnicity, marital status, socioeconomic class, and occupation.
Studies that focus on person can provide information about the magnitude of a problem in different segments of the population, suggest leads about causation, and identify quality-of-care problems. Knowledge that high blood pressure occurs most frequently among blacks, for instance, indicates that it is important that programs to detect hypertension and provide treatment include black populations.
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Knowledge that osteoporosis occurs most frequently in postmenopausal women led to the hypothesis that declining estrogen levels were a cause and hence that estrogen replacement therapy might be used as a prophylactic agent. The observation that mortality following coronary artery bypass surgery is high in hospitals with low surgical volumes suggested that quality of care in these institutions needed to be examined Hannan et al. Key Methodologic Concepts and Issues 37 Descriptive studies of the occurrence of conditions according to "place" might involve examining their frequency within or between natural or political boundaries, in urban versus rural localities, or by latitude.
For example, maps of cancer mortality rates in the United States according to county of residence were first published in Mason et al. These atlases called attention to certain geographic areas with unusually high cancer mortality rates. This led to further research into the reasons for high rates in areas such as New Jersey and the Louisiana Gulf Coast. Similarly, a descriptive study of geographic variation in surgery rates Wennberg and Gittelson was instrumental in initiating formal, critical examination of the reasons for these differences that continue to the present.
Examination of "time" relationships can both identify and evaluate hypotheses related to the causes of changes in conditions. The recent decrease in mortality rates for coronary heart disease in many western countries, for instance, has led to hypotheses about the roles of better diets, decreasing cigarette consumption, better control of hypertension, more physical activity, and improved methods of detection and treatment of coronary heart disease that have become the subject of further research.
The decline in the incidence of Reye syndrome in the time period following a Public Health Service and American Academy of Pediatrics recommendation to avoid use of aspirin to treat children with respiratory illness, chickenpox, and fever provided evidence that aspirin use and Reye syndrome are causally linked.
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Descriptive studies often combine assessment of trends in relation to both time and place. Figure shows time trends in the incidence of advanced HIV disease from through in two areas of Los Angeles County that have been heavily burdened by the epidemic. It shows that incidence rates are declining in all of the affected areas. Analytic Studies Case-Control Studies Case-control studies are those in which persons with a specified condition the cases and persons without the condition the controls are selected for study.
The proportion of cases and of controls with certain characteristics or who have had the exposure of interest is then measured and compared For a 38 Applied Epidemiology Figure Annual incidence of advanced HIV disease AIDS per , population in three Los Angeles communities, ; Source: Los Angeles Department of Health Services numerical characteristic such as blood pressure, the mean level in the cases may be compared to the mean level in the controls. Newly occurring cases are preferred in order to maximize the likelihood that the exposure of interest preceded the condition rather than occurred as a consequence of the disease, and to make sure that rapidly fatal cases and cases of short duration are not underrepresented in the case group.
Controls are most commonly selected from the general population from which the cases came, from people who live in the same neighborhood as the cases, or from among patients seeking medical care for other diseases at the same facilities as the cases. Case-control studies have been extensively used in etiologic research. Their use to assess the adverse effects of drugs and other therapies is also common. Studies of the case-control design have been used with increasing frequency to evaluate the efficacy of preventive interventions Selby et al.
Case-control studies can be carried out relatively quickly, usually do not require as large a sample size as cohort studies to be described later , and are less expensive as a result. For a rare event, they are usually the only practical type of hypothesis-testing study. Table summarizes the results of four Table It would be very costly and probably impossible to conduct four different cohort studies of vaccine efficacy because of the rarity of pneumococcal illness. The data from these three of the four case-control studies find a lower odds ratio for pneumococcal illness in persons who had been vaccinated, providing strong evidence for a benefit of pneumococcal vaccination in adults.
Case-control studies are subject to certain limitations, which have been described in detail by Sackett and Austin et al.
Among the common concerns: Accurate information on the exposure may not be available either from a person's memory or from records. Accurate information on other relevant variables such as confounders and effect modifiers, to be discussed below may not be available.
Patients may search for a cause for their condition and therefore be more likely to report an exposure than controls a form of recall bias, to be described below.