In Funnel Signal Studio we ask people to print their cohort definition in a sentence a non-analyst can read. The sentence usually dies in the first clause. “Users who installed in March” is not a definition. Installed according to which store? Deduplicated how? What happens to the person who already had the app, deleted it, and came back on a new handset?
Membership drift
The most common lie is retroactive membership. A team adds a property — plan tier, country, “is_employee” — and rebuilds last quarter’s curve. The old guests leave; new guests arrive; the line looks calmer. Nobody is cheating in the theatrical sense. They have simply changed the room and kept the photograph’s caption.
A second drift is quieter. Identity graphs stitch two devices into one person after week three. The cohort shrinks. Retention appears to improve because the denominator lost its indecisive members. If you celebrate that improvement in a board pack without a footnote, you have used App Analytics as interior design.
Windows that flatter
Seven days is not a moral number. It is a habit inherited from web dashboards and weekly stand-ups. An app whose value accrues on a payday cycle will look sick on a seven-day window and merely seasonal on a thirty-five-day one. Neither window is “true”. Each excludes a different kind of absence.
We ask Studio Seat people to publish two windows side by side for one quarter and to write which absences they are willing to ignore. The exercise is unpopular. It is also the one alumni mention when they talk about Retention Cartography later.
The honest caption
If you take nothing else from this note, take a caption: who entered, which clock started, which identity rule applied, and what you changed since the last time you showed the same picture. That caption belongs above the chart, not in a appendix nobody opens. App Analytics that cannot survive a caption is not ready for a decision.
We do not claim this makes the numbers larger. It makes them answerable. If you want a template, the Retention Atlas collects the sentences we keep returning to; they are not magic. They are just written down.