 This paper examines the use of self-reported menstrual bleeding data versus data collected from a menstrual tracking application. It found that while both methods yielded similar results, the application provided more accurate data on period length and flow volume. Additionally, it showed that women who overestimated their period length were more likely to underestimate their flow volume, suggesting that this could lead to underdiagnosis of heavy menstrual bleeding. This article was authored by Amanda A. Shea, Thorella Wiva, Cecile Ventola, and others.