Units of "Coverage" variable?

[Jessilyn]

We believe there may be an error in the units reported for the "coverage" variable:

hrv : minutes : value : coverage -  Data completeness in terms of the number of interbeat intervals.

Reported here: https://dev.fitbit.com/build/reference/web-api/intraday/get-hrv-intraday-by-interval

The units are reported as minutes, but looking at the range of data, it seems that the correct units should be Hz. Can someone confirm the correct units?

Thank you!

[Gordon-C]

Hi @Jessilyn 

Let me look into this for you.

[Gordon-C]

Hi @Jessilyn ,

I confirmed with engineering that the documentation is correct.   Coverage is a measure of "completeness", or how many data points are used in the 5 minute interval.   

What makes you think the value returned should be in Hz?

[Jessilyn]

Thanks for this information Gordon! We are looking at data from ~2,000 people in a study and we see left skewed data for the Coverage variable ranging from 0.7 to 1.86 with most of the data is between 0.7 and 1 and a small proportion of values >1. We are trying to understand how best to interpret these values.

We were assuming that HRV calculations are based on beat-to-beat intervals, so we are also wondering how it is possible that a fixed interval of time (e.g., 5 minutes) could be evaluated for Coverage if the variable being assessed is an HRV calculation with a variable interval length. Is there perhaps some sort of interpolation being done to yield equal-interval data? If so, could you please point us to documentation on that? We don't see anything about this on the Fitbit website (https://dev.fitbit.com/build/reference/web-api/intraday/get-hrv-intraday-by-interval). Thank you!

[Gordon-C]

Hi @Jessilyn 

I spoke to engineering and they said all responses should be < 1.  So, I'm filling a bug for this problem.  I'll notify you when the problem is fixed.

[Jessilyn]

Thank you Gordon, we appreciate it!