The 10-day window is mainly a tradeoff between sensitivity and detection speed. Shorter windows give faster results but are much noisier; longer windows give more statistical power but could take weeks to flag a change.
Also, it isn’t comparing one 10-day period once and calling it done. The window rolls forward daily, and a change has to clear the pre-registered 99% threshold in two consecutive windows before it’s flagged.
Ten days isn’t sacred, though. Once there’s enough longitudinal data, one of the things I want to evaluate is whether that window length is actually well calibrated or should be changed in a future version.
Also, it isn’t comparing one 10-day period once and calling it done. The window rolls forward daily, and a change has to clear the pre-registered 99% threshold in two consecutive windows before it’s flagged.
Ten days isn’t sacred, though. Once there’s enough longitudinal data, one of the things I want to evaluate is whether that window length is actually well calibrated or should be changed in a future version.