Table 1.

Descriptive statistics for study participants with and without sleep problems by cohort

Score/value	Non-demented elderly		Poss/prob AD
Score/value	SP+ (N = 325)	SP− (N = 74)	SP+ (N = 73)	SP− (N = 190)
Age (years)	83.6 ± 7.3^†††	81.5 ± 8.7	74.8 ± 12.6	73.7 ± 11.5
Sex (% female)^‡	68.9	58.8	53.4	54.2
Education (years)	13.2 ± 2.7^††	14.1 ± 2.7^***	14.2 ± 3.3	13.4 ± 3.3^*
Duration of AD (years)			5.2 ± 3.0	4.4 ± 2.8^*
Mini-mental state exam (MMSE)	28.1 ± 1.5^†††	28.2 ± 1.5	18.7 ± 7.2	19.4 ± 6.0
ADL	0.3 ± 0.7^†††	0.2 ± 0.6	3.5 ± 3.7	2.2 ± 2.9^*
IADL	0.1 ± 0.4^†††	0.8 ± 0.7	7.6 ± 5.1	6.6 ± 4.3
Cornell Depression Scale	2.2 ± 1.7^†††	1.3 ± 1.6^**	5.2 ± 3.3	3.2 ± 3.2^***
Sleep score (sum of 20 SDSQ ratings)^§	22.5 ± 6.8	15.9 ± 7.6^***	23.3 ± 8.6	14.7 ± 7.8^***
Number of endorsed symptoms	7.6 ± 2.6	5.0 ± 2.9^***	7.4 ± 2.9	4.5 ± 2.8^***
Estimated nighttime time in bed (TIB in h)	8.1 ± 1.2^†††	8.1 ± 1.1	9.3 ± 1.8	9.0 ± 1.4
Percentage of group with ≤ 6 h TIB^a	8.2	5.6	2.8	3.8

Non-demented elderly (NDE) are healthy elderly subjects with normal cognitive function at the time of sleep symptom assessment. Poss/prob AD: individuals met NINCDS-ADRDA criteria for possible or probable Alzheimer’s disease. Sample sizes given reflect number of respondents, however, the numbers for whom each variable were recorded varied. SP+, Endorsed ‘sleep problems’; SP−, did not endorse ‘sleep problems’; ADL, Activities of Daily Living; IADL, Instrumental Activities of Daily Living.

^***

P ≤ 0.001;

^**

P < 0.01;

P < 0.05 across SP+, SP− within cohort;

^†††

P < 0.001;

^††

P < 0.01 across SP+ (across cohorts).

^‡

Chi-squared contingency test and inference tests are Mann–Whitney non-parametric comparisons of means.

^§

‘Awakens feeling well rested’ and ‘have sleep problems’ were excluded from this score.