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What are the advantages and disadvantages of studying disease using a case-control study

Field Epidemiology Manual

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.

  • However, the two studies are methodologically different in that the case—control study starts from the outcome and goes 'back' to determine the exposure to the risk factor, while the cohort study starts from the exposure status and goes 'forward' to determine the incidence of outcome in the groups to be compared;
  • The cohort studies start from the exposure to the risk factor status and compare the incidence of the disease in the exposed and not exposed groups;
  • New England Journal of Medicine, 354 6 , 579-587.

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.

Advantages and Disadvantages of Case-Control 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.

  • His continuous support and valuable feedback on each article were instrumental in improving the quality of the articles;
  • However, the cohort studies are more expensive and require a longer time as well as a larger sample size; the loss to follow-up and misclassification biases can affect the results of the cohort studies;
  • Does the study use matching or pairing appropriately to avoid the effects of a confounding variable?

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.

Case Control Study

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.

  1. However, the two studies are methodologically different in that the case—control study starts from the outcome and goes 'back' to determine the exposure to the risk factor, while the cohort study starts from the exposure status and goes 'forward' to determine the incidence of outcome in the groups to be compared. Instead, the appropriate statement for a case—control study should be that 'there is an association between the disease and the risk factor' or 'cases are 2 times more likely to be exposed to the risk factor as compared to controls'.
  2. Case control studies are observational because no intervention is attempted and no attempt is made to alter the course of the disease.
  3. This may also be due to the fact that during the follow-up period, the exposure status of the subjects may change leading to inappropriate analysis of the results.
  4. It is important to note that case—control study designs cannot determine neither the prevalence or incidence of the disease nor the risk factors as the subjects are generally collected by purposive sampling. It is likely that people who are diseased cases remember their exposure to the risk factor more accurately as compared to the controls.

New England Journal of Medicine, 354 6579-587. 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, 98 151-60. 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.