American Journal of Epidemiology Advance Access published online on October 10, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm265
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Practice of Epidemiology |
Accuracy of Reporting of Menstrual Cycle Length
1 Epidemiology Branch, National Institute of Environmental Health Sciences, Durham, NC
2 Biostatistics Branch, National Institute of Environmental Health Sciences, Durham, NC
3 Epidemiology Support, Westat, Durham, NC
Correspondence to Anne Marie Zaura Jukic, Epidemiology Branch, National Institute of Environmental Health Sciences, PO Box 12233, Durham, NC 27709 (e-mail: jukica{at}niehs.nih.gov).
Received for publication May 21, 2007. Accepted for publication August 17, 2007.
There are many studies based on self-reported menstrual cycle length, yet little is known about the validity of this measure. The authors used data collected in 1990 from 352 women born in Chicago, Illinois, aged 37–39 years. Women reported their usual cycle length and behavioral and reproductive characteristics at study enrollment and then completed daily menstrual diaries for up to 6 months. The authors compared this observed cycle length (geometric mean) with the reported length by using kappa coefficients. To assess systematic effects, they performed linear regression of the difference between reported and observed cycle length. Agreement between observed and reported cycle length was moderate. The crude overall kappa coefficient was 0.33; the kappa adjusted for within-woman sampling variability was 0.45 (95% confidence interval: 0.36, 0.55). On average, women overestimated their cycle length by 0.7 days (95% confidence interval: 0.3, 1.0). Reporting by sexually active women and women with a history of infertility was more accurate. Parity, body mass index, prior medical evaluation for irregular cycles, and exercise were all associated with systematic reporting differences. Studies that rely on self-reported cycle length could be prone to artifactual findings because of systematic covariate effects on reporting.
interviews; menstrual cycle; questionnaires; reproducibility of results; research design
Abbreviations: DES, diethylstilbestrol
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