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Increasing the number of controls above the number of cases, up to a ratio of about 4 to 1, may be a cost-effective way to improve the study.A prospective study watches for outcomes, such as the development of a disease, during the study period and relates this to other factors such as suspected risk or protection factor(s).Case-Control Study A case-control study is a retrospective study that looks back in time to find the relative risk between a specific exposure (e.g. The goal is figure out the relationship between risk factors and disease or outcome and estimate the odds of an individual getting a disease or experiencing an event.
The potential relationship of a suspected risk factor or an attribute to the disease is examined by comparing the diseased and nondiseased subjects with regard to how frequently the factor or attribute is present (or, if quantitative, the levels of the attribute) in each of the groups (diseased and nondiseased)." For example, in a study trying to show that people who smoke (the attribute) are more likely to be diagnosed with lung cancer (the outcome), the cases would be persons with lung cancer, the controls would be persons without lung cancer (not necessarily healthy), and some of each group would be smokers.
If a larger proportion of the cases smoke than the controls, that suggests, but does not conclusively show, that the hypothesis is valid.
A retrospective study, on the other hand, looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study.
Many valuable case-control studies, such as Lane and Claypon's 1926 investigation of risk factors for breast cancer, were retrospective investigations.
With Chegg Study, you can get step-by-step solutions to your questions from an expert in the field. - Includes many concepts such as sample size, hypothesis tests, or logistic regression, explained by Stephanie Glen, founder of Statistics How To.
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.If the outcome of interest is uncommon, however, the size of prospective investigation required to estimate relative risk is often too large to be feasible.In retrospective studies the odds ratio provides an estimate of relative risk.Case-control studies have four main steps: Advantages A case-control study is often the best choice for rare conditions or diseases.Let’s say 10 people in Duval county in Florida had a particularly rare disease.Case–control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the "cases") with patients who do not have the condition/disease but are otherwise similar (the "controls").They require fewer resources but provide less evidence for causal inference than a randomized controlled trial.The study usually involves taking a cohort of subjects and watching them over a long period.The outcome of interest should be common; otherwise, the number of outcomes observed will be too small to be statistically meaningful (indistinguishable from those that may have arisen by chance).Numbers of cases and controls do not have to be equal.In many situations, it is much easier to recruit controls than to find cases.