Table 2. Mixed model results: predictors of sleep quality.

Model Parameter	Units	β	95% CI (lower)	95% CI (upper)	t	p	Cohen’s f2
Intercept	Mean PSQI Score at Post-Baseline	4.50	3.76	5.24	11.95	<.001
Pre-Baseline	Dummy coded contrast with Post-Baseline	0.60	0.18	1.02	2.82	.005	0.040†
Exam Period	Dummy coded contrast with Post-Baseline	0.62	0.08	1.16	2.26	.025	0.040†
Sex	Female	−0.20	−0.87	0.46	−0.60	.548	0.001
Age	Years	−0.034	−0.171	0.102	−0.50	.620	0.000
Health Status	Ill/injured compared to healthy	−0.36	0.24	−0.96	−1.19	.237	0.010
Alcohol	Drinks/week	−0.030	−0.070	0.010	−1.47	.142	0.021
Caffeine	Units/week	0.026	−0.011	0.063	1.39	.165	0.005
Nicotine	Cigarettes/week	0.020	0.007	0.032	3.16	.002	0.018
Perceived Stress	Score (mean centered)	0.054	0.042	0.067	8.47	<.001	0.140

Estimated unstandardized coefficients (β) of the mixed model, with corresponding t-tests against the null-hypothesis of no effect. The mixed model included a random intercept term for each participant. Positive beta values indicate an increase in PSQI score and therefore a decrease in sleep quality. All co-variates were mean-centered. †Value represents effect size of factor time.