A study began in 1970 with a group of 5000 adults in Delhi who were asked about their alcohol consumption. The occurrence of cancer was studied in this group between 1990-1995. This is an example of :
A. Cross-sectional study
B. Retrospective cohort study
C. Concurrent cohort study
D. Case-control study
Correct answer : C. Concurrent cohort study
In a concurrent study (prospective study), the outcome under study has not yet occurred when the study starts. It requires long term follow up. Attrition is a big problem. It is an expensive study.