Religious Pluralism Index

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.