Nested case control design

1. Nested case–control study
(Case-control in a cohort)
Dr Vinodh Kumar O.R
Senior Scientist
ICAR-Indian Veterinary Research Institute
Izatnagar, Bareilly-243122

2. • Variation of a case–control study.
• NCC design overcomes some of the disadvantages associated with
case-control studies, while incorporating some of the advantages of
cohort studies.

3. • Nested case–control study is more efficient than the full cohort design since
design is often used when the exposure of interest is difficult or expensive
to obtain and when the outcome is rare.
• NCC is a retrospective study type that uses an existing cohort study

4. • H0: antipsychotic drugs were associated with venous thromboembolism.
• Data: UK QResearch primary care database consisting of 72,67,673 patients.
• Cases : Adult patients with a first ever record of venous thromboembolism between 1 January
1996 and 1 July 2007.
• Control: For each case, up to four controls were identified, matched by age, calendar time, sex,
and practice.
• 25,532 eligible cases (15,975 with deep vein thrombosis and 9,557 with pulmonary embolism)
and 89,491 matched controls.

5. Example
• As an example, of the 91,523 women in the Nurses' Health Study who did not have
cancer at baseline and who were followed for 14 years, 2,341 women had developed
breast cancer by 1993. Several studies have used standard cohort analyses to study
precursors to breast cancer, e.g. use of hormonal contraceptives,[3] which is a covariate
easily measured on all of the women in the cohort. However, note that in comparison to
the cases, there are so many controls that each particular control contributes relatively
little information to the analysis.
• If, on the other hand, one is interested in the association between gene expression and
breast cancer incidence, it would be very expensive and possibly wasteful of precious
blood specimen to assay all 89,000 women without breast cancer. In this situation, one
may choose to assay all of the cases, and also, for each case, select a certain number of
women to assay from the risk set of participants who have not yet failed (i.e. those who
have not developed breast cancer before the particular case in question has developed
breast cancer). The risk set is often restricted to those participants who are matched to
the case on variables such as age, which reduces the variability of effect estimates.

6. Case–cohort study
• Cases and controls are drawn from within a prospective study.
• All cases who developed the outcome of interest during the follow-up
are selected and compared with a random sample of the cohort.