Cohort windows that fit a high-street app
A cohort is a promise about time. Most App Analytics defaults promise a Californian week: install on any day, look seven days later, draw a curve, call it science. High-street products in the United Kingdom do not live that week. They live bank holidays, late-night shopping, payday Fridays, and a December that starts in November whether you like it or not.
I sat with a regional grocer last spring whose “D7 retention” collapsed every time an install landed on a Thursday. The product was a list-and-collect app. Households that installed on Thursday often intended to shop on Saturday. Measuring them on the following Thursday meant measuring them after a shop that had already happened, and before the next one. The curve looked like churn. The diary looked like a family.
The fix was not a cleverer chart. The fix was a window that started at first completed collect, not at first open, and that lasted until the next expected shop — fourteen days for most of their catchments, seven for the inner-city stores that turn faster. That window would be wrong for a cosmetics retailer. It would be wrong for a travel app. It was right for them, which is the only compliment a window deserves.
Start clocks on behaviour
Install is a distribution event. First open is a curiosity event. First completed job — a collect, a booking, a lesson, a transfer — is usually the product. If you start the cohort clock on curiosity, you will spend the rest of the quarter explaining noise.
In the United Kingdom you must also name the calendar. Half-term is not an outlier; it is a season. August is not “summer” in the way a global dashboard means summer. A Signal Note that ignores school holidays for an education-adjacent app is not incomplete. It is incorrect.
Throw splits away
Once you have a window, you will be tempted to split by everything: device, source, weather, loyalty card. Retention Cartography in our studio insists that you keep two splits and delete the rest. A split that does not change a decision is a hobby. Hobbies are allowed at home. They are expensive in a meeting.
If you want a supervised version of this argument, the four-week Retention Cartography desk exists for it. If you only needed the reminder: stop importing weeks that were never yours.