Takeshi Minakawa* Charapla Inc., Yokohama, Japan
*Correspondence: [info-www.charapla.net]
November 24, 2025
[日本語]
Permanent Archive (Internet Archive)
https://osf.io/fy8zp/files/ywv7k
Abstract
AbstractBackground: The belief that the frequency of births increases during the full moon or new moon (the so-called “lunar effect”) persists among the general public and some medical professionals, despite a lack of established medical evidence. Objective: The purpose of this study is to verify whether lunar phases have a statistical influence on birth rates using a large-scale dataset of over 100,000 Japanese individuals. Methods: We analyzed birth data from 135,748 individuals collected via the entertainment web service “charapla.net” between 2010 and 2017. The lunar age (0–29) at birth was calculated for each individual. Expected frequencies were derived from a calendar-based simulation to account for the variation in the duration of lunar phase categories. The goodness-of-fit was analyzed using the Chi-square test and Cohen’s w for effect size. Results: The distribution of births across lunar ages was extremely flat. No specific increase in births was observed around the full moon or new moon. Although a statistically significant difference was detected (χ2(29) = 55.43, p = 0.0022), the effect size was negligible (Cohen’s w = 0.02). Conclusion: The results statistically demonstrate that there is no substantial association between lunar phases and birth rates in the contemporary Japanese population.
Continue reading “Absence of Correlation Between Lunar Phases and Birth Rates: A Statistical Analysis of 135,000 Japanese Individuals”
