Over 96.9% of the population of Azerbaijan is nominally Muslim. (Estimates include 96.9% Muslim (CIA), 93.4% (Berkley Center, 2012), 99.2% (Pew Research Center, 2009).) The rest of the population adheres to other faiths or are non-religious, although they are not officially represented. Among the Muslim majority, religious observance varies and Muslim identity tends to be based more on culture and ethnicity rather than religion. The Muslim population is approximately 85% Shi'a and 15% Sunni; differences traditionally have not been defined sharply. The Republic of Azerbaijan has the second highest Shia population percentage in the world after Iran.