Supplementary Material for: A Cross-Sectional Growth Reference and Chart of Stretched Penile Length for Japanese Boys Aged 0-7 Years

<b><i>Background/Aim:</i></b> Reference values for penile length have not been established for Japanese boys. We aimed to develop percentiles and means (and standard deviations) of stretched penile length (SPL) in Japanese boys. <b><i>Methods:</i></b> A cross-sectional study was performed in 1,628 Japanese boys aged <9 years from 2007 through 2014. The LMS method was used to develop a growth reference and chart for SPL in boys aged 0-7 years. Interobserver variation in SPLs was assessed in 32 boys (aged 0-11 years, median 3 years) using the Bland-Altman plot. The correlation between SPL and stature, weight or body mass index (BMI) was analyzed by the Pearson test. <b><i>Results:</i></b> SPL increases continuously during the prepubertal period, and most rapidly in the first 4 months of life. No significant fixed or proportional bias was found for interobserver variation (p = 0.5; r<i> = </i>0.33, p = 0.06). There was no significant correlation between SPL z-score and stature z-score (r<i> = </i>0.14, p < 0.001), weight z-score (r<i> = </i>0.09, p < 0.001) or BMI z-score (r = 0.01, p = 0.71). <b><i>Conclusion:</i></b> These data serve as an updated growth reference for SPL in Japanese boys aged 0-7 years.