Cohort Analysis is an aggregate method that describes cases in terms of the time of a common critical event (birth cohorts group individuals based on date of birth).  Cohorts are assumed to share attitudes and behaviors based on this commonality.

Cohort theories assume developmental models in which each cohort manifests similar characteristics as they reach the same time since entry.  Cohorts may also differ from one another in predictable ways based on their experience of differing contexts or events.