Compare methods

	Religious Pluralism Index	Religious Vitality Index
Field	Sociology Of Religion	Sociology Of Religion
Family	Process / pipeline	Process / pipeline
Year of origin	2002	1994
Originator	David Voas, Daniel V. A. Olson & Alasdair Crockett (critique); religious-economies tradition	Laurence R. Iannaccone
Type	Diversity/concentration index for religious composition	Index/model of religious group strength via strictness
Seminal source	Voas, D., Olson, D. V. A., & Crockett, A. (2002). Religious Pluralism and Participation: Why Previous Research Is Wrong. American Sociological Review, 67(2), 212-230.	Iannaccone, L. R. (1994). Why Strict Churches Are Strong. American Journal of Sociology, 99(5), 1180-1211.
Aliases	Religious Diversity Index, Religious Fractionalization Index, Herfindahl Religious Concentration Index, Denominational Pluralism Index	Church Strength Index, Strictness-Vitality Measure, Religious Group Strength Model, Free-Rider Vitality Index
Related	3	3
Summary	The religious pluralism index measures how religiously diverse a population is by computing the probability that two randomly selected people belong to different religious groups. It is the religious application of the Herfindahl-Hirschman concentration measure: one minus the sum of squared denominational shares, ranging from zero (a single dominant group) toward one (many evenly sized groups). The index became central to the sociology of religion because the religious-economies paradigm predicted that greater pluralism, by signaling competition among firms, should raise participation. David Voas, Daniel Olson, and Alasdair Crockett's 2002 American Sociological Review article showed that much of the prior literature testing this claim was undermined by a mathematical artifact linking the index to participation, making careful construction and interpretation of the index a methodological topic in its own right.	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.