Introduction to study designs - case-control studies Introduction Learning objectives: You will learn about basic introduction to case-control studies, its analysis and interpretation of outcomes. Case-control studies are one of the frequently used study designs due to the relative ease of its application in comparison with other study designs. This section introduces you to basic concepts, application and strengths of case-control study.
Case Control Study Definition A study that compares patients who have a disease or outcome of interest cases with patients who do not have the disease or outcome controlsand 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.
The goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: These studies are designed to estimate odds.
Case control studies are also known as "retrospective studies" and "case-referent studies. Controls should be subjects who might have been cases in the study but are selected independent of the exposure. Cases and controls should also not be "over-matched.
Does the study use matching or pairing appropriately to avoid the effects of a confounding variable? Does it use appropriate inclusion and exclusion criteria? Fictitious Example There is a suspicion that zinc oxide, the white non-absorbent sunscreen traditionally worn by lifeguards is more effective at preventing sunburns that lead to skin cancer than absorbent sunscreen lotions.
A case-control study was conducted to investigate if exposure to zinc oxide is a more effective skin cancer prevention measure.
The study involved comparing a group of former lifeguards that had developed cancer on their cheeks and noses cases to a group of lifeguards without this type of cancer controls and assess their prior exposure to zinc oxide or absorbent sunscreen lotions. This study would be retrospective in that the former lifeguards would be asked to recall which type of sunscreen they used on their face and approximately how often.
This could be either a matched or unmatched study, but efforts would need to be made to ensure that the former lifeguards are of the same average age, and lifeguarded for a similar number of seasons and amount of time per season.
Real-life Examples Chambers, C.
Selective serotonin-reuptake inhibitors and risk of persistent pulmonary hypertension of the newborn. New England Journal of Medicine, 6 This study used a matched design, matching infants who had persistent pulmonary hypertension with infants who did not have it, and compared the rates of exposure to SSRIs.
Autoimmune and chronic inflammatory disorders and risk of non-hodgkin lymphoma by subtype. Journal of the National Cancer Institute, 98 1 This study matched patients with non-Hodgkin lymphoma NHL with control subjects and compared their history of autoimmune and chronic inflammatory disorders, markers of severity, and treatment.
This study looked at the relation between risk of acute myocardial infarction and current or former smoking, type of tobacco, amount smoked, effect of smokeless tobacco, and exposure to secondhand smoke.The above study was a population based case-control study, with all babies born with a cleft lip in Norway between and identified as cases and with a sample of controls selected at random from the Norwegian medical birth registry for the same period.
A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest).
In theory, the case-control study can be described simply. First, identify the cases (a group known to have the outcome) and the controls (a group known to be. Case-control study.
Case-control studies start with the outcome of interest, for example, a disease, and then look backward in time to detect possible causes or risk factors for that disease.
In a large and carefully controlled Swedish study, their use invites information bias.
Case proxies may either overreport or underreport past. Selection bias occurs in case-control studies when cases and/or controls are selected on criteria related to the exposure of interest, i.e. they are selected differentially on the basis of their exposure status or there may be differences in reporting of exposure status between cases and controls.
Note that in case-control studies the measurement of exposure is established after the development of disease and as a result is prone to both recall and observer bias. The above study was a population based case-control study, with all babies born with a cleft lip in Norway between and identified as cases and with a sample of controls selected at random from the Norwegian medical birth registry for the same period.