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Six Dynamics of Religious Change



As religious demographers once and awhile we have to get serious about method. This short reflection below is at the core of our methodology in understanding how religious populations grow or decline. We hope the simple diagram and explanation leaves you with another set of tools to use in navigating statistics of religious affiliation. Have fun!

The dynamics of change in religious affiliation can be reduced to three sets of empirical population data that together enable enumeration of the increase or decrease in adherents over time. To measure overall change, these three sets can be defined as follows: (1) births minus deaths; (2) converts to minus converts from; and (3) immigrants minus emigrants. The first variable in each of these three sets (births, converts to, immigrants) measures increase, whereas the second (deaths, converts from, emigrants) measures decrease. All future (and current) projections of religious affiliation, within any subset of the global population (normally a country or region), will account for these dynamics, and the changes themselves are dependent on these dynamics.


The primary mechanism of global religious demographic change is (live) births. Children are almost always counted as having the religion of their parents (as is the law in Norway, for example). In simple terms, if populations that are predominantly Muslim, for example, have more children on average than those that are predominantly Christian or Hindu, then over time (all other things being equal) Muslims will become an increasingly larger percentage of that population. This means that the relative size of a religious population has a close statistical relationship to birthrates.


Even as births increase their memberships, religious communities experience constant loss through the deaths of members. Though this often includes tragic, unanticipated deaths of younger members, it most frequently affects the elderly members. Thus, changes in health care and technology can positively impact religious communities if members live longer.

Births minus deaths/total fertility rate

The change over time in any given population is most simply expressed as the number of births into the community minus the number of deaths out of it. Many religious communities around the world experience little else in the dynamics of their growth or decline. Detailed projections rely on a number of estimated measures, including life expectancy, population age structures, and the total fertility rate. This means that any attempt to understand the dynamics of religious affiliation must be based firmly on demographic projections of births and deaths.

Converts to

It is a common observation that individuals (or even whole villages or communities) change allegiance from one religion to another (or to no religion at all). In some countries, legal and social consequences make conversion difficult, and survey respondents might be reluctant to speak honestly about the topic. In particular, Hinduism is for many Hindus (as is Islam for many Muslims) not just a religion but also an ethnic or cultural identity that does not depend on whether a person actively practises the faith. Thus even non-practising or secular Hindus may still consider themselves, and be viewed by their neighbours, as Hindus.

Converts from

Conversion to a new religion, as mentioned above, also involves conversion from a previous one. Thus, a convert to Islam is, at the same time, a convert from another religion. In the twentieth and twenty-first centuries, the most converts from Christianity were and continue to be found largely among those in the Western world who have decided to be agnostics or atheists.

Converts to minus converts from

The net conversion rate in a population is calculated by subtracting the number of converts from the number of converts to. Conversion to and conversion from will likely continue to play a role in changing religious demographics in the future.


Equally important at the international level is how the movement of people across national borders impacts religious affiliation. Once religious communities are established through immigration they often grow vigorously (for a time) via high birth rates.


In a reversal of nineteenth-century European colonization of Africa, Asia, and parts of the Americas, the late twentieth century witnessed waves of emigration of people from these regions to the Western world. The impact on religious affiliation is significant.

Immigrants minus emigrants

In the twenty-first century, international migration continues to have a significant impact on the religious composition of individual countries. One can try to anticipate the way in which expected immigration and emigration trends will affect a country’s population over time. One profound change to be expected is the increase of religious pluralism in almost every country of the world. Increasing religious pluralism is not always welcomed and can be seen as a political, cultural, national, or religious threat.

The six dynamics discussed above determine changes in religious demographics. Gains are the result of three positive dynamics: births, conversions to, and immigration. Losses are the result of three negative dynamics: deaths, conversions from, and emigration. The net change in religious demographics is the result of gains minus losses. Any attempt to understand religious affiliation in the past, present, or future must be firmly based on demographic dynamics. A proper awareness of these dynamics and their significance is thus vital both for undertaking and for interpreting studies of the future of religion.