Sleep disturbances and sleep-related impairments were assessed
using the validated Patient Reported Outcomes Measurement Information
System (PROMIS) Sleep Disturbance and Sleep-Related Impairments
Scales (Buysse, 2010). These scales measure self-reported sleep
disturbances (trouble falling or staying asleep) and sleep-related
daytime impairments (difficulty functioning due to poor sleep) in the
past 7 days, and are normalized on a T distribution with a mean of 50
and standard deviation of 10. The Cronbach's alphas at baseline were
0.90 and 0.92, respectively, indicating good reliability of the scales.