ARIC indicates Atherosclerosis Risk in Communities study; CHS, Cardiovascular Health Study; FHS, Framingham Heart Study; MrOS, Osteoporotic Fractures in Men Study; N1, stage N1 sleep; N2, stage N2 sleep; OSA, obstructive sleep apnea; REM, rapid eye movement; SME, sleep maintenance efficiency; SOF, Study of Osteoporotic Fractures; SWS, slow wave sleep; T90, percentage of sleep time with oxygen saturation less than 90%; TST, total sleep time; WASO, wake after sleep onset.