Introduction to study designs - case-control studies Introduction Learning objectives:
Events Study Designs This short article gives a brief guide to the different study types and a comparison of the advantages and disadvantages. A defined population P from which groups of subjects are studied Outcomes O that are measured And for experimental and analytic observational studies: Interventions I or exposures E that are applied to different groups of subjects Overview of the design tree 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. Tree of different types of studies Q1, 2, and 3 refer to the three questions below Download a PDF by Jeremy Howick about Study Designs Our first distinction is whether the study is analytic or non-analytic.
A non-analytic or descriptive study does not try to quantify the relationship but tries to give us a picture of what is happening in a population, e. 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.
An analytic study attempts to quantify the relationship between two factors, that is, the effect of an intervention I or exposure E on an outcome O. To quantify the effect we will need to know the rate of outcomes in a comparison C group as well as the intervention or exposed group.
Whether the researcher actively changes a factor or imposes uses an intervention determines whether the study is considered to be observational passive involvement of researcheror experimental active involvement of researcher.
In experimental studies, the researcher manipulates the exposure, that is he or she allocates subjects to the intervention or exposure group.
Experimental studies, or randomised controlled trials RCTsare similar to experiments in other areas of science. That is, subjects are allocated to two or more groups to receive an intervention or exposure and then followed up under carefully controlled conditions.
Such studies controlled trials, particularly if randomised and blinded, have the potential to control for most of the biases that can occur in scientific studies but whether this actually occurs depends on the quality of the study design and implementation. In analytic observational studies, the researcher simply measures the exposure or treatments of the groups.
These studies all include matched groups of subjects and assess of associations between exposures and outcomes. Observational studies investigate and record exposures such as interventions or risk factors and observe outcomes such as disease as they occur. Such studies may be purely descriptive or more analytical.
We should finally note that studies can incorporate several design elements. For example, a the control arm of a randomised trial may also be used as a cohort study; and the baseline measures of a cohort study may be used as a cross-sectional study. Spotting the Study Design The type of study can generally be worked at by looking at three issues as per the Tree of design in Figure 1: What was the aim of the study?
If analytic, was the intervention randomly allocated? Observational study For observational study the main types will then depend on the timing of the measurement of outcome, so our third question is: When were the outcomes determined?
Some time after the exposure or intervention? Best for study the effect of an intervention.Design and Analysis of Case-Control Studies Kyoungmi Kim, Ph.D. Nov 9 & 16, Different types of controls may be used, and they have different limitations. Types of Controls Analysis of Case-Control Studies.
Case Control Studies:Patients who already have a certain condition are compared with people who do plombier-nemours.com control studies are generally designed to estimate the odds (using an odds ratio) of developing the studied condition/disease.
Case series and Case reports consist of collections of reports on the treatment of individual patients or a report on a single patient.
Because they are reports of cases and use no control groups to compare outcomes, they have little statistical validity.
Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.
In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature. Types of Study Designs Meta-Analysis A way of combining data from many different research studies.
A meta-analysis is a statistical process that combines the findings from individual studies. Case-control Study Case-control studies begin with the outcomes and do not follow people over time. Researchers choose people with a particular result. Case Control Studies:Patients who already have a certain condition are compared with people who do plombier-nemours.com control studies are generally designed to estimate the odds (using an odds ratio) of developing the studied condition/disease.
Understanding Research Study Designs. There are certain types of questions on which randomized.