Table 3.

Final Hierarchical Linear Model of Association between Sleep Behavior Variables, Fatigue and the Diurnal Cortisol Rhythm (N = 130).

Fixed Effects	Coefficient	SE	Interpretation
Cortisol Intercept (Wakeupa)
Intercept	−1.216***	0.066	Awakening level = 0.296b
MFSI	0.154*	0.081	14% increase per +1SD
PSQI	−0.067	0.497	---
Nap duration	−0.184**	0.062	17% decrease per +1SD
Nocturnal awakenings	0.088*	0.044	9% increase per +1SD
Latency to fall asleep	0.009	0.008	---
Morning restfulnessc	−0.187**	0.062	17% decrease per +1SD
Linear Time Slope
Intercept	−0.191***	0.013	17% decrease per hr at wakeupd
MFSI	0.035*	0.016	3.4% flatter
PSQI	0.026**	0.009	2.7% flatter
Nap duration	−0.035***	0.009	3.4% steeper
Nocturnal awakenings	−0.021	0.012	---
Latency to fall asleep	−0.013***	0.002	1.3% steeper
Morning restfulness	0.023*	0.011	2.3% flatter
Co-morbidity Index	0.004**	0.002	0.4% flatter
Quadratic Time Slope
Intercept	0.004***	0.0007	0.4% Increase per hr2
MFSI	0.0009	0.0011	---
PSQI	−0.0015	0.0011	---
Nap duration	−0.0017**	0.0005	0.1% less curvature
Nocturnal awakenings	0.0009	0.0009	---
Latency to fall asleep	0.0007**	0.0001	0.07% more curvature
Morning restfulness	0.0005	0.0008	---
Cortisol Awakening Response (CAR)
Intercept	0.394***	0.039	48% increase 30-min post wakeup
MFSI	−0.146**	0.050	13.5% decrease per +1SD
PSQI	−0.002	0.051	---
Nap duration	0.042*	0.021	4.3% increase per +1SD
Nocturnal awakenings	−0.029	0.043	---
Latency to fall asleep	0.009	0.008	---
Morning restfulness	0.124**	0.049	12% increase per +1SD

Notes. ^aTime was coded 0 at the wakeup time.

^bBecause cortisol values were natural-log transformed, the inverse of that transformation (the exponential function) was applied to return the intercept to the original scale of measurement.

^cHigher Morning restfulness score indicates lower levels of feeling rested on the morning of saliva collection.

^dLinear time slope intercept represents instantaneous rate of change at awakening. All Level 1 predictors are uncentered; Level 2 and Level 3 predictors are either standardized or grand-mean centered. MFSI= Multidimensional Fatigue Symptom Inventory, PSQI= Pittsburgh Sleep Quality Inventory.

^***p < .001,

^**p < .01,

^*p ≤ .05.