Epidemiological Study Designs Advantages And Disadvantages Pdf
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A study that compares patients who have a disease or outcome of interest cases with patients who do not have the disease or outcome controls , and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease. Case control studies are observational because no intervention is attempted and no attempt is made to alter the course of the disease.
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Epidemiologists use primary and secondary data sources to calculate rates and conduct studies. Primary data is the original data collected for a specific purpose by or for an investigator. For example, an epidemiologist may collect primary data by interviewing people who became ill after eating at a restaurant in order to identify which specific foods were consumed.
Collecting primary data is expensive and time-consuming, and it usually is undertaken only when secondary data is not available. Secondary data is data collected for another purpose by other individuals or organizations.
Examples of sources of secondary data that are commonly used in epidemiological studies include birth and death certificates, population census records, patient medical records, disease registries, insurance claim forms and billing records, public health department case reports, and surveys of individuals and households.
Descriptive epidemiology is used to characterize the distribution of disease within a population. It describes the person, place, and time characteristics of disease occurrence. Analytical epidemiology, on the other hand, is used to test hypotheses to determine whether statistical associations exist between suspected causal factors and disease occurrence. It also is used to test the effectiveness and safety of therapeutic and medical interventions. The tests of analytical epidemiology are carried out through four major types of research study designs: cross-sectional studies, case-control studies , cohort studies, and controlled clinical trials.
Cross-sectional studies are used to explore associations of disease with variables of interest. For example, a cross-sectional study designed to investigate whether residential exposure to the radioactive gas radon increases the risk of lung cancer may examine the level of radon gas in the homes of lung cancer patients.
Cross-sectional studies have the advantage of being inexpensive and simple to conduct. Their main disadvantage is that they establish associations at most, not causality. Case-control studies start with people with a particular disease cases and a suitable control group without the disease and then compare the two groups for their exposure to the factor that is suspected of having caused the disease.
Case-control studies are most useful for ascertaining the cause of rare events, such as rare cancers. Case-control studies have the advantages of being quick to conduct and inexpensive, and they require only a small number of cases and controls.
Their main disadvantage is that they rely on recall, which may be biased , or on records to determine exposure status. Cohort studies are observational studies in which a defined group of people the cohort is followed over time and outcomes are compared for individuals who were exposed or not exposed to a factor at different levels. Cohorts can be assembled in the present and followed into the future a concurrent cohort study or identified from past records a historical cohort study.
The main advantage of cohort studies is that they identify the timing and directionality of events. Their main disadvantages are that they require large sample sizes and long follow-up times.
They also are not suitable for investigating rare diseases. Controlled clinical trials are studies that test therapeutic drugs or other health or medical interventions to assess their effectiveness and safety.
A controlled clinical trial compares the outcome of a new drug or intervention given to an experimental group with a control group that does not receive the same drug or intervention. To minimize bias, individuals involved in clinical trials may be randomly assigned to the experimental and control groups. In many countries, new therapeutic agents and medical devices are subject to rigorous controlled clinical trials before they are made available to the public.
A major advantage of controlled clinical trials is that they provide unbiased results; however, they are very expensive to conduct. Epidemiology Article Media Additional Info. Article Contents. Load Previous Page. Sources of epidemiological data Epidemiologists use primary and secondary data sources to calculate rates and conduct studies.
Descriptive and analytical epidemiology Descriptive epidemiology is used to characterize the distribution of disease within a population. Ross M. The interaction of host and parasite populations constitutes the subject matter of epidemiology the term being more inclusive than suggested by its relation to the word epidemic.
In most instances the epidemiology of infectious disease is characteristic of that disease and is an outgrowth…. Coronary heart disease is the leading cause of death worldwide, although its occurrence is unevenly distributed. It is one of the most common causes of death in North America and Europe. Epidemiology is the study of the distribution of disease in different populations. Prevalence denotes the number of cases of a condition present at a particular time or over a specified period, while incidence denotes the number of new cases occurring in a defined time period.
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Case Control Study
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What is epidemiology? What can epidemiology tell us? How are epidemiology studies conducted? What are the different types of epidemiology study designs? What are the limitations of epidemiology studyies? How are the results of epidemiology studies interpreted?
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Cohort studies are the analytical design of observational studies that are epidemiologically used to identify and quantify the relationship between exposure and outcome. Due to the longitudinal design, cohort studies have several advantages over other types of observational studies. The purpose of this chapter is to cover the various characteristics of prospective cohort studies. This chapter is divided into three main sections.
We previously discussed descriptive epidemiology studies, noting that they are important for alerting us to emerging health problems, keeping track of trends in the population, and generating hypotheses about the causes of disease. Analytic studies provide a basic methodology for testing specific hypotheses. The essence of an analytic study is that groups of subjects are compared in order to estimate the magnitude of association between exposures and outcomes. This module will build on descriptive epidemiology and on measuring disease frequency and association by discussing cohort studies and intervention studies clinical trials. Our discussion of analytic study designs will continue in module 5 which addresses case-control studies.
Epidemiologists use primary and secondary data sources to calculate rates and conduct studies. Primary data is the original data collected for a specific purpose by or for an investigator. For example, an epidemiologist may collect primary data by interviewing people who became ill after eating at a restaurant in order to identify which specific foods were consumed. Collecting primary data is expensive and time-consuming, and it usually is undertaken only when secondary data is not available. Secondary data is data collected for another purpose by other individuals or organizations. Examples of sources of secondary data that are commonly used in epidemiological studies include birth and death certificates, population census records, patient medical records, disease registries, insurance claim forms and billing records, public health department case reports, and surveys of individuals and households.
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