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Confirmatory factor analysis of the Insomnia Severity Index (ISI) and invariance across race

a pooled analysis of MsFLASH data

Otte, Julie L., PhD, RN1; Bakoyannis, Giorgos, PhD1,2; Rand, Kevin L., PhD3; Ensrud, Kristine E., MD, MPH4; Guthrie, Katherine A., PhD5; Joffe, Hadine, MD, MSc6; McCurry, Susan M., PhD7; Newton, Kathrine M., PhD8; Carpenter, Janet S., PhD, RN, FAAN1

doi: 10.1097/GME.0000000000001343
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Objective: Women's sleep at menopause is widely reported to be problematic. The Insomnia Severity Index (ISI) is a commonly used tool for quantifying sleep problems in clinical and research settings, but psychometric properties in postmenopausal women have not been reported. Our study aim was to examine the factor structure of the ISI in a large and diverse sample of midlife women with hot flashes.

Methods: Baseline data were from 899 women enrolled in one of the three clinical trials using similar entry criteria conducted by the Menopause Strategies Finding Lasting Answers to Symptoms and Health research network. We conducted confirmatory factor analyses for the total sample and within strata defined by race/ethnicity (black and white women).

Results: The ISI had two factors in the total sample. The two-factor structure was consistent across black and white women, with the exception of one item “difficulty falling asleep.”

Conclusions: The ISI in midlife women with hot flashes is composed of two factors that capture dimensions of the insomnia severity and daytime impact. The instrument is a psychometrically sound scale appropriate for use in research and clinical practice to capture the severity and daytime impact of insomnia symptoms in diverse samples of midlife women with hot flashes. An abbreviated screening of two items could be considered to determine if further evaluation is needed of sleep complaints.

1School of Nursing, Indiana University, Indianapolis, IN

2Department of Biostatistics, Fairbanks School of Public Health and School of Medicine, Indiana University, Indianapolis, IN

3Department of Psychology, School of Science, Indiana University-Purdue University Indianapolis, IN

4Medicine and Epidemiology and Community Health, University of Minnesota and Minneapolis VA Health Care System, Minneapolis, MN

5MsFLASH Data Coordinating Center, Fred Hutchinson Cancer Research Center, Seattle, WA

6Connors Center for Women's Health and Gender Biology, Department of Psychiatry, Brigham and Women's Hospital, Harvard Medical School, Boston, MA

7Department of Psychosocial and Community Health, School of Nursing, University of Washington, Seattle, WA

8Kaiser Permanente Washington Health Research Institute, Seattle, WA.

Address correspondence to: Julie L. Otte, PhD, RN, OCN, 600 Barnhill Drive, NU W401, Indianapolis, IN 46202. E-mail: jlelam@iu.edu

Received 6 November, 2018

Revised 6 March, 2019

Accepted 6 March, 2019

Funding/support: The MsFLASH studies were supported by a cooperative agreement issued by the National Institute of Aging (NIA), in collaboration with the Eunice Kennedy Shriver National Institute of Child Health and Development (NICHD), the National Center for Complementary and Alternative Medicine (NCCAM), and the Office of Research and Women's Health (ORWH), and NIA grants U01AG032659, U01AG032669, U01AG032682, U01AG032699, and U01AG032700. In Indiana, this project was supported by the Indiana Clinical and Translational Sciences Institute, funded in part by grant UL1 RR025761 from the National Institutes of Health, National Center for Research Resources, Clinical, and Translational Sciences Award. The content of the manuscript is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Financial disclosure/conflicts of interest: JSC and KLR are funded under an Independent Grant for Learning and Change from Pfizer, Inc (2017-2018). JSC consults for QUE Oncology and Astellas Pharma, Inc. HJ receives grant support from NIH, Merck, Pfizer, Pfizer, and QUE Oncology and consults for KaNDy and Sojournix; and her spouse is a Merck employee. The rest of the authors have no conflicts to report.

© 2019 by The North American Menopause Society.