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Difference Between Case Control Cohort And Cross Sectional Studies Pdf

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Case-control and Cohort studies: A brief overview

Metrics details. We propose a conceptualization of cohort studies in systematic reviews of comparative studies. The main aim of this conceptualization is to clarify the distinction between cohort studies and case series. We discuss the potential impact of the proposed conceptualization on the body of evidence and workload. All studies with exposure-based sampling gather multiple exposures with at least two different exposures or levels of exposure and enable calculation of relative risks that should be considered cohort studies in systematic reviews, including non-randomized studies.

Case–control study

As noted earlier, descriptive epidemiology can identify patterns among cases and in populations by time, place and person. From these observations, epidemiologists develop hypotheses about the causes of these patterns and about the factors that increase risk of disease. In other words, epidemiologists can use descriptive epidemiology to generate hypotheses, but only rarely to test those hypotheses. For that, epidemiologists must turn to analytic epidemiology. The key feature of analytic epidemiology is a comparison group.


Cross sectional studies are used to determine prevalence. They are relatively quick and easy but do not permit distinction between cause and effect. Case controlled studies compare groups retrospectively. They seek to identify possible predictors of outcome and are useful for studying rare diseases or outcomes.


Lesson 1: Introduction to Epidemiology

Cohort and case-control methodologies are the main tools for analytical epidemiological research. Other important types of epidemiological studies mainly for generating hypotheses include cross-sectional and ecological, or correlation studies. The conclusions that can be drawn from findings of these types of studies are, however, much weaker compared to those of cohort and case-control studies. This is not to say that findings from cohort and case-control studies always reflect true associations which can be universally generalized.

A case—control study also known as case—referent study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.

Retrospective cohort study

The prodominant study designs can be categorised into observational and interventional studies. Observational studies, such as cross-sectional, case control and cohort studies, do not actively allocate participants to receive a particular exposure, whilt interventional studies do. Each of the above study designs are described here in turn. In a cross-sectional study, data are collected on the whole study population at a single point in time to examine the relationship between disease or other health-related outcomes and other variables of interest exposures. Cross-sectional studies therefore provide a snapshot of the frequency of a disease or other health-related characteristics in a population at a given point in time.

Cross-sectional study designs are used when studying one or more variables within a given population at one point in time. Such studies are useful for establishing associations rather than causality and for determining prevalence, rather than incidence. In cohort studies, a group of people within a population is followed over a specified period of time to track who experiences or develops the same significant life event or treatment. This type of design can be used "to study incidence, causes, and prognosis. Because they measure events in chronological order they can be used to distinguish between cause and effect.

This short article gives a brief guide to the different study types and a comparison of the advantages and disadvantages. Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational. The list is not completely exhaustive but covers most basics designs. Figure: Tree of different types of studies Q1, 2, and 3 refer to the three questions below. Our first distinction is whether the study is analytic or non-analytic. Descriptive studies include case reports, case-series, qualitative studies and surveys cross-sectional studies, which measure the frequency of several factors, and hence the size of the problem.

Case-control and Cohort studies: A brief overview

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The cohort study design identifies a people exposed to a particular factor and a comparison group that was not exposed to that factor and measures and compares the incidence of disease in the two groups. A higher incidence of disease in the exposed group suggests an association between that factor and the disease outcome. This study design is generally a good choice when dealing with an outbreak in a relatively small, well-defined source population, particularly if the disease being studied was fairly frequent. The case-control design uses a different sampling strategy in which the investigators identify a group of individuals who had developed the disease the cases and a comparison of individuals who did not have the disease of interest. The cases and controls are then compared with respect to the frequency of one or more past exposures. If the cases have a substantially higher odds of exposure to a particular factor compared to the control subjects, it suggests an association.

Posted on 6th December by Saul Crandon. Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence. These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies 1. Although these studies are not ranked as highly as randomised controlled trials, they can provide strong evidence if designed appropriately. Case-control studies are retrospective.

Although the relative risk from a prospective cohort study is numerically approximate to the odds ratio from a case-control study for a low-probability event, a definite relationship between case-control and cohort studies cannot be confirmed. In this study, we established a different model to determine the relationship between case-control and cohort studies. Two analysis models the cross-sectional model and multiple pathogenic factor model were established. Incidences in both the exposure group and the nonexposure group in a cohort study were compared with the frequency of the observed factor in each group diseased and nondiseased in a case-control study. The relationship between the results of a case-control study and a cohort study is as follows: ; , where Pe and Pn represent the incidence in the exposed group and nonexposed group, respectively, from the cohort study, while Pd and Pc represent the observed frequencies in the disease group and the control group, respectively, for the case-control study; finally, m represents the incidence in the total population.

Lesson 1: Introduction to Epidemiology

A retrospective cohort study , also called a historic cohort study , is a longitudinal cohort study used in medical and psychological research. A cohort of individuals that share a common exposure factor is compared with another group of equivalent individuals not exposed to that factor, to determine the factor's influence on the incidence of a condition such as disease or death. Retrospective cohort studies have existed for approximately as long as prospective cohort studies. The retrospective cohort study compares groups of individuals who are alike in many ways but differ by a certain characteristic for example, female nurses who smoke and ones who do not smoke in terms of a particular outcome such as lung cancer. This is fundamentally the same methodology as for a prospective cohort study, except that the retrospective study is performed post-hoc, looking back.

2 Comments

Soren B. 16.03.2021 at 15:37

are used to determine prevalence. They are relatively quick and easy but do not permit.

Leon T. 18.03.2021 at 13:41

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