Case Control Study Example

Netherlands Cohort on Vitamin Intake

Lead Author(s): Jeff Martin, MD

Abstract from Zeegers

(Zeegers' abstract) below is an example from a study that used the case-cohort design.

" Summary in the Netherlands Cohort Study among 120.852 subjects aged 55-69 years at baseline (1996), the association between vitamins and carotenoids intake, vitamin supplement use, and bladder cancer incidence was examined. Exposure status was measured with a food-frequency questionnaire. After 6.3 years of follow-up, data from 550 cases and 3123 subcohort members were avilable for case cohort analysis. The age, sex, and smoking-adjusted relative risks (RRs) for retinol, vitamin E, alpha-carotene, beta-carotene, lutein, and zeaxanthin, and lycopene were 1.04, 0.98, 1.03, 0.99, 1.11, and 1.08, respectively comparing higest to lowest quintile of intake. Only vitamin C (RR: 0.81, 95% CI: 0.61-1.07, P-trend = 0.08) and beta-cryptoxanthin intake (RR: 0.74, 95% CI: 0.53-1.03, P-trend <0.01) were inversely associated with bladder cancer risk. The association with vitamin C disappeared after adjustment for beta-cryptoxanthin but not vice versa. The RRs for supplemental use of vitamin A, C or E compared to no use were around unity."

Study Parameters and Results

This is a very large study in the Netherlands of 120,852 persons followed since 1986. The authors report a relative risk, which is meant as a synonym for risk ratio. This is an instance where a lot of baseline data and baseline biological samples collected for later testing can then be used for studying a number of outcomes just by determining the incidence of diagnoses for that outcome and testing only a random sample (here called a subcohort) of the baseline.

Graphic Netherlands Case Cohort Study

This is a graphic from the Zeegers study.


The efficiency of the design is seen in the need to do biological tests on a limited number of stored serum samples.

Study Variables

Questionnaire variables such as age and gender were captured on everyone in the cohort. For biological measures,


Zeegers, M. P., Goldbohm, R. A., & van den Brandt, P. A. (2001). Are retinol, vitamin C, vitamin E, folate and carotenoids intake associated with bladder cancer risk? Results from the Netherlands Cohort Study. Br J Cancer, 85(7), 977-983.