Month the mammogram was taken and percent mammographic density (%MD) by geographic region of usual area of residence.

¹Usual residence, South, i.e., Akershus and Hordaland counties 60°N and North, i.e., Nordland county 67°N ²n = 268 missing values on month the mammogram was taken(season) ³Least square means adjusted for age (continuous), body mass index (continuous), estrogen and progestin therapy (never, past and current), parity (0, 1,2 or ≥3), Educational level (≤10 years, 11–14 years and ≥15 years) and study year (0 = 2004 or 1 = 2006/07). Month the mammogram was taken and percent mammographic density (%MD) by geographic region of usual area of residence.