Table 2. Zero-order correlations between sleep indicators.

	Total SleepTime	Variability of TotalSleep Time	Wake After SleepOnset	SleepEfficiency	Sleep OnsetLatency
Variability of Total Sleep Time
Combined sample	−.49***
Predominantly White subsample	−.43***
African American subsample	−.47***
Wake After Sleep Onset
Combined sample	−.09*	.25***
Predominantly White subsample	−.06	.18**
African American subsample	.07	.16
Sleep Efficiency
Combined sample	.61***	−.57***	−.65***
Predominantly White subsample	.59***	−.51***	−.64***
African American subsample	.52***	−.52***	−.56***
Sleep Onset Latency
Combined sample	−.35***	.43***	.38***	−.78***
Predominantly White subsample	−.36***	.42***	.24***	−.74***
African American subsample	−.24**	.36***	.37***	−.79***
PSQI: Poor subjective sleep quality
Combined sample	−.13*	.30***	.29***	−.30***	.25***
Predominantly White subsample	−.10	.29***	.18**	−.18**	.16**
African American subsample	.01	.17	.30***	−.26**	.23**

Note. Abbreviations: PSQI: Pittsburgh Sleep Quality Index.

^* P<.05,

^** P<.01,

^*** P<.001.