What your phone already knows about your better days.
Your iPhone has been counting your sleep, steps and heart for years. Drop in its Health export and see which habits really go with better nights and calmer mornings, checked the careful way.
- Open the Health app and tap your picture (top right).
- Tap Export All Health Data, then Save to Files.
- Choose that export.zip below.
Fitbit? Go to takeout.google.com, choose only Fitbit, and export. When the email comes, download the zip and choose it below. If Google split it into several zips, choose them all at once.
Android (Samsung, Pixel, Garmin, Oura and others)? Open Health Connect in Settings, then Backup and restore, Export. Choose the Health Connect.zip it saves.
How it stays honest
Each habit splits your days into "had it" and "didn't", with at least 5 on each side. To rule out runs of good weeks, the habit days are slid against your days by a week or more, every way possible; a gap only counts if it beats nearly all of those. Every comparison is then corrected together (Holm), so trying many things does not make a lucky finding. If the day before was already as good, it says the habit may follow the good days instead of causing them.
Turning points come from weekly averages: a shift counts only if it is far bigger than your weeks normally wander (a CUSUM test that allows for weeks moving together, at the strict 1% level) and lasts at least 8 weeks on each side. The date checker compares the 8 weeks after your date with the 8 weeks before, then asks how often any other date in your history shows a gap that big.
The newest 5 years are checked. A big export can take a minute on a phone. Fitbit's HRV is a different measure from the iPhone's (RMSSD, not SDNN), so compare each only with itself.
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