We distinguish two streams of theory that dominate explanations of religious change: cohort-based cumulative decline theory, which emphasizes small and ongoing declines in individual religiosity accruing across generations; and political backlash theory, which emphasizes period- and identity-based changes due to the politicized meaning of religion. Notably, Muslim countries have largely been excluded from a recent wave of quantitative research on individual-level religious change, implicitly continuing an assumption that Islamic societies require different theoretical concepts.
