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. Author manuscript; available in PMC: 2015 Sep 1.
Published in final edited form as: Psychosom Med. 2014 Sep;76(7):519–528. doi: 10.1097/PSY.0000000000000097

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.

b

Because 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.

c

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

d

Linear 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.