Project Aims & Methodology

In order to put the theoretical discussion about the impact of religious diversity in a broader context, researchers commonly use the religious diversity index. The traditional way of measuring religious diversity is based on membership propotion in accordance to the Herfindahl-Hirschmann index. This index, however, only grossly suits for the analysis of the relation between religious diversity and religious vitality. It therefore bears no distinct value for theories in the sociology of religion whether they favour the market model of religions or opt for secularisation processes. An international research group of the Center for Religious Studies (CERES) has therefore started to calculate religious diversity in a different way by the help of new measuring strategies.

Innovative way of measuring religious diversity

CERES researchers have based their calculations for a new religious diversity index in the joint project Religious Plurality in three European Countries on the adherence diversity index (ADI), the organisational diversity index (ODI) and the centrality of religiosity scale (CRS):

  • The adherence diversity index (ADI) indicates the extent to which the individuals in a particular territory are distributed across the counted religous groups and relates to the diversity of religious memberships.
  • The organisational diversity index (ODI) indicates the extent to which the religious organisations in a particular territory are distributed across different religious traditions.
  • The centrality of religiosity scale (CRS) measures the impact of religious meanings on the feelings, cognitions, and actions of individuals. It refers to five core dimensions of religious life: the ideological, experiental, devotional (as private practice), ritual (public practice), and intellectual dimensions.

This new way of measuring religious diversity was successfully applied for the three different European countries, Finland, Germany, and Slovenia. It helped to answer the question whether religious diversity in these countries has any effect on religious vitality, may it be promoting or prohibiting terms.

Religious diversity by country

In order to overcome the lack of suitable empirical research on religious diversity, CERES researchers have furthermore generated an religious diversity index for each country in the world. The foundation for the indices are empirical data from open databases such as the CIA factbook and the Religion Data Base. Due to the fact, that these databases gather information on religious membership for almost every country under the same conditions, the huge advantage of these indices is that they are more comparable to each other than those generated from independent local research projects. By all the inherent limitations of the sources the CERES religious diversity index by country can at least very roughly illustrate the social, cultural and institutional preconditions for the development and existence of religious diversity.

Visualising religious diversity worldwide

All CERES religious diversity indices by country were edited and visualised in a single world map. Even though the sources have their bold limitations, this map offers a gross overview of how diverse a country is in terms of religions. It is an innovative form of mapping religions in comparison to the territorical blocks of religions one can find on traditional maps.

Please click here to open the map.


Religious Diversity Index


Prof. Dr. Volkhard Krech

CERES, Ruhr-Universität Bochum, Germany

Dr. Kimmo Ketola

Kirkon tutkimuskeskus, Tampere, Finland


Prof. Dr. Stefan Huber

Fakultät für Theologie, Universität Bern, Schweiz