A cohort is a unit of analysis that groups people who joined at the same time or made their first purchase under the same conditions to compare their subsequent behavior. For example, when comparing return visits by initial acquisition channel, the acquisition period and observation period are set to be the same.
Differences between cohorts can arise not only from channels, but also from campaigns, product mix, and seasonal demand. Sample size and loss to follow-up should also be checked. We do not generalize the observed retention differences to a universal superiority or inferiority of any channel.