Do we realy have a good metric for non-clinical normal sleep quality?
At this point the literature and the manufacturers of wareables seem to be at a loss for an accepted standard. We have a pretty good idea what sleep problems look like, and how to classify sleep stages. But can we agree on a metric to distinguish better sleep from good sleep?
I think we have a pretty good standard. Sleep happens in cycles during the night and IMHO spending the most time in the deep sleep stage as possible is what matters most to sleep quality. This is where the garbage collection process takes place to get rid of all the sensory clutter from the day.
I would also include having very few, optimally zero, sleep interruptions during the night because of apnea or periodic limb movement in a quality of sleep metric.