Explanation:
A cohort refers to a group of organisms which share a defined characteristic.
Cohort study involves study of these cohorts and gathering data at particular interval of time.
In cohort study, a group of individual with same characteristic are chosen and certain data such as their life history, advent of disease and their effect are recorded.
Cohort study can be defined as a longitudinal study because it involves the repeated observation of same factor again and again..
Cohort studies do not involve any control set up. It provides an advantage by allowing to study the effect of a number of exposures simultaneously.