[jerlam]

This would also depend on how she's carrying the iPhone. While putting the GPS receiver on your wrist isn't optimal, putting the iPhone in a pocket or somewhere closer and lower on the body where it sees even less of the sky is worse.

[brippalcharrid]

My experience of using Strava on a mid-range Android phone several years ago was that readings were splayed horizontally across (road-side) paths by five or ten meters in many cases. Now that I have a Garmin watch, I am gradually closing in on my former Estimated Best Efforts with readings that appear to be much more accurate in terms of how they correspond to the paths that I've been running on.

[lifeinthevoid]

She wears it around her waist, might explain a lot. Thanks for the pointer!