If the software compares behavior between nights and can then say "that was relatively good", then you're right and the limitation matters If the software beha

If the software compares behavior between nights and can then say "that was relatively good", then you're right and the limitation matters If the software behaves no differently from one night to the next, that is, if you can take any random night's assessment and it would be as likely to be accurate as the first, then it does not matter that they had participants only wear it one night. You'd get more data (from multiple nights) without needing to recruit more participants, but you'd also be biasing towards whether the tracker works well for this set of people (probably a worthwhile trade-off, up to a point) Your watch says to use it for a while. It could be that that's just because it's not flawless and they want people to see it's often correct even if they got unlucky the first night(s). Or maybe your watch works differently from the ones used in this study I'm also surprised they only did one night, both because you get a lot more data per amount of effort by having participants keep it for a month, and because I'd not be surprised if the software is more comparative than absolute. But I don't know if we can draw real conclusions from that