So what I mean is that if you observe something like this:
Then it seems that there is no overall trend over time, just fluctuations. When fitbit count is high, then sleep quality is also high. Randomly but correlating. Which is interesting
. The intention is that if such thing is observed, and, say, sleep quality is important - then this is interesting. Then try to vary the fitbit count on purpose - walk less, walk more - and see if the sleep quality follows. That way causality can be established.