Dynamic Cohort

A dynamic cohort is one whose membership is recomputed each time the report runs, so users join and leave it as their behaviour changes.

It is defined by a rule rather than by a list; what gets stored is the condition, such as at least five visits in the past thirty days, and the resulting population differs every day. Its counterpart is the static cohort, which freezes the member list at build time. The frequent error is comparing two runs of the same dynamic cohort on different dates and attributing the difference to changed behaviour, when the population itself changed; following one fixed group over time calls for a static cohort.