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The objective of this study was to evaluate the construct validity of the five-item Women’s Health Initiative Insomnia Rating Scale (WHIIRS) by comparing women taking hormone therapy (HT) versus those taking a placebo and by comparing women known to differ in vasomotor symptoms.The WHIIRS was included in two phase III randomized trials intended to evaluate the efficacy of a combination estradiol plus and norethindrone acetate transdermal delivery system in reducing vasomotor symptoms. In all, 850 healthy postmenopausal women participated in these studies. Both trials were double-blind, one was placebo-controlled and the other was positive-controlled. The former trial admitted women with ≥8 hot flashes/day and lasted 12 weeks with data collected on the WHIIRS at baseline, 4, 8, and 12 weeks. The other trial had no entry criteria pertaining to hot flashes and lasted 52 weeks with WHIIRS data collected at baseline, 12, 24, and 52 weeks.The WHIIRS was sensitive to the effect of HT on sleep disturbance over time. The WHIIRS also detected differences in self-reported sleep disturbance between women with mild vasomotor symptoms compared with those with moderate to severe symptoms. As expected, the study using a positive control revealed that sleep improved over time (p <.0001). Also as predicted, the study using a placebo control found that sleep disturbance in the treatment groups improved at a faster rate than in the control groups (p = .035).The construct validity of the WHIIRS was supported because it was successfully used to detect self-reported sleep disturbance differences in women taking HT versus those taking a placebo as well as in groups known to differ in severity of their vasomotor symptoms.