Table 2.

Polysomnography variables (mean ± S.D.) in the four ethnic groups.

	African-American (n = 13)	Asian-American (n = 18)	Mexican-American (n = 19)	Non-Hispanic White (n = 46)	SES	Ethnicity
Sleep continuity					1.89	3.35**
Total sleep time (min)	456.6 ± 48.9	487.8 ± 32.6	471.3 ± 37.9	472.6 ± 44.6		1.87
Sleep latency (min)	14.5 ± 9.2	13.8 ± 9.0	12.1 ± 5.6	15.2 ± 11.1		0.23
Sleep efficiency (%)	92.3 ± 2.2a	94.1 ± 1.7b	94.4 ± 2.2b	94.5 ± 2.6b		3.10*
Arousals	23.1 ± 9.5	22.9 ± 9.6	19.2 ± 8.3	20.7 ± 8.4		0.83
Awake time (min)	18.6 ± 13.7	19.3 ± 10.4	13.9 ± 8.8	17.7 ± 10.1		0.80
Sleep architecture					0.28	4.26***
Stage 1 sleep (%)	10.8 ± 4.7	9.8 ± 4.0	8.3 ± 2.9	10.1 ± 4.7		0.98
Stage 2 sleep (%)	58.2 ± 7.2a	52.8 ± 6.6b	48.9 ± 9.3b	52.4 ± 6.7b		4.09**
Stage 3 sleep (%)	9.4 ± 3.1	12.0 ± 4.9	12.1 ± 6.4	10.3 ± 4.3		1.36
Stage 4 sleep (%)	5.0 ± 5.3a	9.5 ± 6.5b	10.3 ± 5.4b	10.0 ± 5.8b		2.77*
REM sleep (%)	16.7 ± 3.1a	16.0 ± 3.7a	20.4 ± 3.9b	17.3 ± 3.3a		5.61****
REM measures
1st REM episode					0.74	1.25
REM latency (min)a	104.1 ± 50.7	99.5 ± 22.8	103.1 ± 46.1	102.6 ± 35.0		–
REM activity (units)	10.4 ± 12.2	16.6 ± 9.7	16.4 ± 10.1	17.3 ± 13.9		–
REM density (units/min)	1.4 ± 0.5	1.6 ± 0.5	1.5 ± 0.4	1.6 ± 0.5		–
REM duration (min)	7.0 ± 6.7	9.7 ± 5.4	10.4 ± 5.3	10.1 ± 6.2		–
REM measures
All REM episodes combined					0.67	4.27***
REM activity (units)a	160.1 ± 76.1	176.5 ± 53.1	243.8 ± 101.9	175.3 ± 82.9		1.02
REM density (units/min)	2.2 ± 1.0	2.3 ± 0.6	2.6 ± 0.8	2.1 ± 0.8		2.32
REM duration (min)	76.4 ± 16.2a	78.1 ± 18.7a	94.1 ± 18.9b	81.4 ± 20.9a		2.73*
Number of REM episodes	4.1 ± 0.5	4.0 ± 0.5	4.4 ± 0.5	4.2 ± 0.6		1.32

^aAnalyses were performed on log-transformed data.

^*p ≤ .05.

^**p ≤ .01.

^***p ≤ .005.

^****p ≤ .001.