The NORFACE research team around Volkhard Krech published an important article earlier this year. It investigates the connection between religious diversity and religious vitality more thoroughly than previous studies and develops a more complex measuring model.
The article is available online - and for free. Just go the IJRR's website: http://www.religjournal.com/
Krech, Volkhard, Markus Hero, Stefan Huber, Kimmi Ketola, and Richard Traunmüller. "Religious Diversity and Religious Vitality: New Measuring Strategies and Empirical Evidence." Interdisciplinary Journal of Research on Religion 9 (2013): Article 3. http://www.religjournal.com/articles/article_view.php?id=70
Quantitative studies of the conditions and consequences of religious diversity are based mostly on indices that measure the variety of religious membership in a particular region. However, this line of research has become stagnant, and the question of whether diversity affects religious vitality remains unanswered. This article attempts to shed new light on the discussion by measuring religious diversity differently and capturing religious vitality independently of membership figures. In particular, it contrasts the Herfindahl-Hirschman Index based on membership proportions with a second measure of diversity: an index of organizational diversity. Conversely, the dependent variable religious vitality is measured not by using rates of participation in religious organizations but via the Centrality of Religion Scale. Based on ecological and individual level data of forty-three local regions in Finland, Germany, and Slovenia and using multilevel analysis, our results suggest that religious diversity is related to religious vitality. However, the nature of this association differs across subgroups.