Sleep stage accuracy

[CanadaB]

According to my Fitbit my sleep is better than I expected as far as how much deep sleep I'm getting. I know that fitbits aren't 100% accurate for sleep stages but is there anyone who understands the science better than I do that can tell me exactly how accurate they are? Like if my fitbit says I had 30 mins of deep sleep at a certain part of the night, is it possible I didnt get any deep sleep at all? Is the fit it accurate enough that I can assume I did get some deep sleep but maybe just the duration of the deep sleep is off by a bit?

[LZeeW]

@CanadaB   Sorry that no one responded before.  I found this article in Runner's World.   I'l let you judge for yourself.

[n8vz]

Sometimes my Fitbit seems quite inaccurate in determining sleep stages.  Today, for instance, I got a low score of 71, even though I slept through the night pretty soundly, and had a better than average perceived sleep quality.  My average Fitbit sleep score is in the mid 80s.  Last night it said I had only one period of deep sleep and almost no REM sleep.  

I found this article, the only academic study I could find on the subject, which indicates Fitbit’s algorithm often underestimates the transition from one sleep stage to another.  I think that’s what happened to me last night.

https://pubmed.ncbi.nlm.nih.gov/31172956/