Results would vary for each person, but sleep may help in another way, too.
Results can vary from one trial to another, and analysis is needed to understand why.
When many studies of one problem are conducted, the results can vary.
But the results vary so much even within a town that the solution is to test.
Results can vary wildly over a short period of time.
Lots of analysis is based around trying to explain why your results vary.
However, the result can vary for different order of chains.
Again the results varied from the first test, but matched the second.
The results over the years have varied wildly in quality.
Also, the driver will use the results to vary how they drive on that particular track.