Table 2.

Means, standard deviations, score frequency, and corrected item-total correlation for each component of the PSQI.

PSQI Component	M	SD	Score Frequency (%)				rtot
			0	1	2	3
Subjective sleep quality	1.4	0.8	10.4	45.8	35.3	8.5	0.64
Sleep latency	1.7	1.1	21.4	23.9	22.4	32.3	0.52
Sleep duration	1.3	0.9	20.9	33.8	36.3	9.0	0.61
Habitual sleep efficiency	1.2	1.2	37.3	24.9	16.9	20.9	0.66
Sleep disturbances	1.4	0.6	3.0	55.2	37.8	4.0	0.42
Use of sleep medication	0.7	1.1	72.6	6.0	5.5	15.9	0.24
Daytime dysfunction	1.3	0.9	19.9	37.8	35.8	6.5	0.32
Total Cronbach’s α							0.75
Mean inter-item correlation coefficient							0.317

Note: PSQI = Pittsburgh Sleep Quality Index; M = mean; SD = standard deviation; r^tot = corrected item-total correlation.