Table 3.

Estimated effect of the lighting intervention (blue light mask) in delaying sleep onset based on actigraphy measurements.

Effect of interventiona	Estimate (min)	SE	DF	t value	Pr > |t|
All participants (N = 46)
Overall Treatment Effect	−0.4	7.5	1411	−0.05	0.96
Periodb	16.5	7.5	1411	2.19	0.029
Intervention	1.9	6.7	1423	0.29	0.78
Control	2.3	7.6	1420	0.31	0.76
Carryover of intervention	−12.2	9.8	1423	−1.24	0.21
Carryover of control	−15.5	10.3	1423	−1.51	0.13
Participants compliant with light mask (n = 23)
Overall Treatment Effect	−1.6	8.1	860	−0.20	0.84
Periodb	6.5	4.1	860	1.59	0.11
Intervention	−5.9	7.6	859	−0.78	0.44
Control	−4.2	8.1	859	−0.53	0.60
Carryover of intervention	−8.9	10.9	866	−0.81	0.42
Carryover of control	−11.0	10.8	863	−1.02	0.31
Participants compliant with light mask + Actiwatch (n = 17)
Overall Treatment Effect	−9.2	9.9	640	−0.93	0.35
Periodb	19.3	9.9	640	1.95	0.052
Intervention	−13.5	9.7	639	−1.39	0.17
Control	−4.3	9.1	639	−0.47	0.64
Carryover of intervention	−9.9	14.0	645	−0.71	0.48
Carryover of control	−18.6	12.7	641	−1.47	0.14

Notes:

^(a)Overall treatment effect = shift in bed time attributable to the blue light intervention relative to the control condition (red light), adjusting for period effects and crossover effects, as well as random effects in a linear mixed model; Intervention effect = blue light mask trial period compared with baseline; Control effect = red light mask trial period compared with baseline. Sleep parameters measured using accelerometers (Actiwatch) worn by study participants. All analyses controlled for period and carryover effects.

^(b)Estimate shown is twice estimated regression coefficient due to cell mean coding for period.

Analyses were performed using SAS, version 9 (SAS Institute, Cary, NC).