Ch. 10 Case Control Studies
Nested Case -control Studies:
-In such the controls are a sample of individuals who are at risk for the disease at the time each case of the disease develops. -in this way, the cases and controls are matched on calendar time and length of follow up.
Case Control Study Design process
-Select persons with a health condition (cases) -select persons without the condition (controls) -measure PAST exposure (review medical records, questionnaire, interview participants)
Case Control studies deign overview-
-observational in nature -from an outcome (disease) to a previous exposure -important to have a solid case definition - aiming to examine the relationship between outcome and exposure
Case-control studies abased in a Defined Cohort
A population is identified and followed over time. At the time of the population is identified, baseline data are obtained from records or interviews, from blood or urine tests. The population is then followed for a period of years . In both nested case control and case cohort design, cases and controls are derived from the same original cohort so likelier to have greater comparability between the cases and the controls than traditional case control. -Nested Case-control Studies -cohort case control studies
Case control studies vs. cohort
case control studies are generally less expensive, and can be carried out more quickly thus they are often the first step in determining whether an exposure is linked to an increased risk of disease ( 1st step in searching for a cause of adverse health effect) -case control studies also valuable when the disease being investigated is rare. Cohorts need many years of follow up, more expensive,
Case-Cohort studies:
cases develop at the same times that were seen in the nested case control study but the controls are randomly chosen from the defined cohort with which the study began. Advantage: since controls are not individually matched to each case, it is possible to study different diseases(different set of cases) in the same case cohort study using the same cohort for controls. Cases and controls are not matched on calendar time and length of follow up - instead exposure is characterized for the subcohort.
case-crossover design
used for studying the etiology of acute outcomes such as myocardial infarctions or deaths from acute events in situations where the suspected exposure is transient and its effect over over a short time. - each person who is a case serves as his own control with the period immediately before his adverse outcome being compared with a "control" period at a prior time time when no adverse outcome occuured
Advantages of Embedding a Case-Control Study in Defined Cohort:
1) eliminates recall bias 2) better comparability coming from same cohort 3) cheaper
Difference between cohort and case-control
Case-control study begins with people with the disease ( cases) and compares them to people without the disease (controls). Contrasts to cohort studies which begins with a group of exposed people and compares them to a nonexposed group.
