Religious Vitality Index

The religious vitality index operationalizes Laurence Iannaccone's celebrated argument, in his 1994 American Journal of Sociology article 'Why Strict Churches Are Strong,' that demanding religious groups are often the most vital. The seeming paradox dissolves once religion is viewed as a collective good vulnerable to free-riding: if members can enjoy the fellowship, enthusiasm, and mutual support of a congregation while contributing little, average commitment erodes and the group weakens. Strictness - costly, distinctive demands such as dress codes, time obligations, and behavioral prohibitions - works as a screening device that drives out the half-hearted and raises the average commitment of those who remain. The vitality index therefore models a group's strength as a function of its strictness, its members' participation, and its capacity to retain and mobilize committed adherents.