The Changing Religious Affiliation Projections. Muslims Will Have Much Greater Impact

APRIL 2, 2015

The Future of World Religions: Population Growth Projections, 2010-2050

Why Muslims Are Rising Fastest and the Unaffiliated Are Shrinking as a Share of the World’s Population

The religious profile of the world is rapidly changing, driven primarily by differences in fertility rates and the size of youth populations among the world’s major religions, as well as by people switching faiths. Over the next four decades, Christians will remain the largest religious group, but Islam will grow faster than any other major religion. If current trends continue, by 2050 …

• The number of Muslims will nearly equal the number of Christians around the world.
• Atheists, agnostics and other people who do not affiliate with any religion – though increasing in countries such as the United States and France – will make up a declining share of the world’s total population.
• The global Buddhist population will be about the same size it was in 2010, while the Hindu and Jewish populations will be larger than they are today.
• In Europe, Muslims will make up 10% of the overall population.
• India will retain a Hindu majority but also will have the largest Muslim population of any country in the world, surpassing Indonesia.
• In the United States, Christians will decline from more than three-quarters of the population in 2010 to two-thirds in 2050, and Judaism will no longer be the largest non-Christian religion. Muslims will be more numerous in the U.S. than people who identify as Jewish on the basis of religion.
• Four out of every 10 Christians in the world will live in sub-Saharan Africa.

These are among the global religious trends highlighted in new demographic projections by the Pew Research Center. The projections take into account the current size and geographic distribution of the world’s major religions, age differences, fertility and mortality rates, international migration and patterns in conversion.

As of 2010, Christianity was by far the world’s largest religion, with an estimated 2.2 billion adherents, nearly a third (31%) of all 6.9 billion people on Earth. Islam was second, with 1.6 billion adherents, or 23% of the global population.

If current demographic trends continue, however, Islam will nearly catch up by the middle of the 21st century. Between 2010 and 2050, the world’s total population is expected to rise to 9.3 billion, a 35% increase.1 Over that same period, Muslims – a comparatively youthful population with high fertility rates – are projected to increase by 73%. The number of Christians also is projected to rise, but more slowly, at about the same rate (35%) as the global population overall.

As a result, according to the Pew Research projections, by 2050 there will be near parity between Muslims (2.8 billion, or 30% of the population) and Christians (2.9 billion, or 31%), possibly for the first time in history.2

With the exception of Buddhists, all of the world’s major religious groups are poised for at least some growth in absolute numbers in the coming decades. The global Buddhist population is expected to be fairly stable because of low fertility rates and aging populations in countries such as China, Thailand and Japan.

Worldwide, the Hindu population is projected to rise by 34%, from a little over 1 billion to nearly 1.4 billion, roughly keeping pace with overall population growth. Jews, the smallest religious group for which separate projections were made, are expected to grow 16%, from a little less than 14 million in 2010 to 16.1 million worldwide in 2050.

Adherents of various folk religions – including African traditional religions, Chinese folk religions, Native American religions and Australian aboriginal religions – are projected to increase by 11%, from 405 million to nearly 450 million.

And all other religions combined – an umbrella category that includes Baha’is, Jains, Sikhs, Taoists and many smaller faiths – are projected to increase 6%, from a total of approximately 58 million to more than 61 million over the same period.3

While growing in absolute size, however, folk religions, Judaism and “other religions” (the umbrella category considered as a whole) will not keep pace with global population growth. Each of these groups is projected to make up a smaller percentage of the world’s population in 2050 than it did in 2010.4

Similarly, the religiously unaffiliated population is projected to shrink as a percentage of the global population, even though it will increase in absolute number. In 2010, censuses and surveys indicate, there were about 1.1 billion atheists, agnostics and people who do not identify with any particular religion.5 By 2050, the unaffiliated population is expected to exceed 1.2 billion. But, as a share of all the people in the world, those with no religious affiliation are projected to decline from 16% in 2010 to 13% by the middle of this century.

At the same time, however, the unaffiliated are expected to continue to increase as a share of the population in much of Europe and North America. In the United States, for example, the unaffiliated are projected to grow from an estimated 16% of the total population (including children) in 2010 to 26% in 2050.

As the example of the unaffiliated shows, there will be vivid geographic differences in patterns of religious growth in the coming decades. One of the main determinants of that future growth is where each group is geographically concentrated today. Religions with many adherents in developing countries – where birth rates are high, and infant mortality rates generally have been falling – are likely to grow quickly. Much of the worldwide growth of Islam and Christianity, for example, is expected to take place in sub-Saharan Africa. Today’s religiously unaffiliated population, by contrast, is heavily concentrated in places with low fertility and aging populations, such as Europe, North America, China and Japan.

Globally, Muslims have the highest fertility rate, an average of 3.1 children per woman – well above replacement level (2.1), the minimum typically needed to maintain a stable population.6 Christians are second, at 2.7 children per woman. Hindu fertility (2.4) is similar to the global average (2.5). Worldwide, Jewish fertility (2.3 children per woman) also is above replacement level. All the other groups have fertility levels too low to sustain their populations: folk religions (1.8 children per woman), other religions (1.7), the unaffiliated (1.7) and Buddhists (1.6).

Another important determinant of growth is the current age distribution of each religious group – whether its adherents are predominantly young, with their prime childbearing years still ahead, or older and largely past their childbearing years.

In 2010, more than a quarter of the world’s total population (27%) was under the age of 15. But an even higher percentage of Muslims (34%) and Hindus (30%) were younger than 15, while the share of Christians under 15 matched the global average (27%). These bulging youth populations are among the reasons that Muslims are projected to grow faster than the world’s overall population and that Hindus and Christians are projected to roughly keep pace with worldwide population growth.

All the remaining groups have smaller-than-average youth populations, and many of them have disproportionately large numbers of adherents over the age of 59. For example, 11% of the world’s population was at least 60 years old in 2010. But fully 20% of Jews around the world are 60 or older, as are 15% of Buddhists, 14% of Christians, 14% of adherents of other religions (taken as a whole), 13% of the unaffiliated and 11% of adherents of folk religions. By contrast, just 7% of Muslims and 8% of Hindus are in this oldest age category.

In addition to fertility rates and age distributions, religious switching is likely to play a role in the growth of religious groups. But conversion patterns are complex and varied. In some countries, it is fairly common for adults to leave their childhood religion and switch to another faith. In others, changes in religious identity are rare, legally cumbersome or even illegal.

The Pew Research Center projections attempt to incorporate patterns in religious switching in 70 countries where surveys provide information on the number of people who say they no longer belong to the religious group in which they were raised. In the projection model, all directions of switching are possible, and they may be partially offsetting. In the United States, for example, surveys find that some people who were raised with no religious affiliation have switched to become Christians, while some who grew up as Christians have switched to become unaffiliated. These types of patterns are projected to continue as future generations come of age. (For more details on how and where switching was modeled, see the Methodology. For alternative growth scenarios involving either switching in additional countries or no switching at all, see Chapter 1.)

Over the coming decades, Christians are expected to experience the largest net losses from switching. Globally, about 40 million people are projected to switch into Christianity, while 106 million are projected to leave, with most joining the ranks of the religiously unaffiliated. (See chart above.)

All told, the unaffiliated are expected to add 97 million people and lose 36 million via switching, for a net gain of 61 million by 2050. Modest net gains through switching also are expected for Muslims (3 million), adherents of folk religions (3 million) and members of other religions (2 million). Jews are expected to experience a net loss of about 300,000 people due to switching, while Buddhists are expected to lose nearly 3 million.

International migration is another factor that will influence the projected size of religious groups in various regions and countries.

Forecasting future migration patterns is difficult, because migration is often linked to government policies and international events that can change quickly. For this reason, many population projections do not include migration in their models. But working with researchers at the International Institute for Applied Systems Analysis in Laxenburg, Austria, the Pew Research Center has developed an innovative way of using data on past migration patterns to estimate the religious composition of migrant flows in the decades ahead. (For details on how the projections were made, see Chapter 1.)

The impact of migration can be seen in the examples shown in the graph at the right, which compares projection scenarios with and without migration in the regions where it will have the greatest impact. In Europe, for instance, the Muslim share of the population is expected to increase from 5.9% in 2010 to 10.2% in 2050 when migration is taken into account along with other demographic factors that are driving population change, such as fertility rates and age. Without migration, the Muslim share of Europe’s population in 2050 is projected to be nearly two percentage points lower (8.4%). In North America, the Hindu share of the population is expected to nearly double in the decades ahead, from 0.7% in 2010 to 1.3% in 2050, when migration is included in the projection models. Without migration, the Hindu share of the region’s population would remain about the same (0.8%).

In the Middle East and North Africa, the continued migration of Christians into the six Gulf Cooperation Council (GCC) countries (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates) is expected to offset the exodus of Christians from other countries in the region.7 If migration were not factored into the 2050 projections, the estimated Christian share of the region’s population would drop below 3%. With migration factored in, however, the estimated Christian share is expected to be just above 3% (down from nearly 4% in 2010).

Beyond the Year 2050

This report describes how the global religious landscape would change if current demographic trends continue. With each passing year, however, there is a chance that unforeseen events – war, famine, disease, technological innovation, political upheaval, etc. – will alter the size of one religious group or another. Owing to the difficulty of peering more than a few decades into the future, the projections stop at 2050.

Readers may wonder, though, what would happen to the population trajectories highlighted in this report if they were projected into the second half of this century. Given the rapid projected increase from 2010 to 2050 in the Muslim share of the world’s population, would Muslims eventually outnumber Christians? And, if so, when?

The answer depends on continuation of the trends described in Chapter 1. If the main projection model is extended beyond 2050, the Muslim share of the world’s population would equal the Christian share, at roughly 32% each, around 2070. After that, the number of Muslims would exceed the number of Christians, but both religious groups would grow, roughly in tandem, as shown in the graph above. By the year 2100, about 1% more of the world’s population would be Muslim (35%) than Christian (34%).

The projected growth of Muslims and Christians would be driven largely by the continued expansion of Africa’s population. Due to the heavy concentration of Christians and Muslims in this high-fertility region, both groups would increase as a percentage of the global population. Combined, the world’s two largest religious groups would make up more than two-thirds of the global population in 2100 (69%), up from 61% in 2050 and 55% in 2010.

It bears repeating, however, that many factors could alter these trajectories. For example, if a large share of China’s population were to switch to Christianity (as discussed in this sidebar), that shift alone could bolster Christianity’s current position as the world’s most populous religion. Or if disaffiliation were to become common in countries with large Muslim populations – as it is now in some countries with large Christian populations – that trend could slow or reverse the increase in Muslim numbers.

Regional and Country-Level Projections

In addition to making projections at the global level, this report projects religious change in 198 countries and territories with at least 100,000 people as of 2010, covering 99.9% of the world’s population. Population estimates for an additional 36 countries and territories are included in regional and global totals throughout the report. The report also divides the world into six major regions and looks at how each region’s religious composition is likely to change from 2010 to 2050, assuming that current patterns in migration and other demographic trends continue.8

Due largely to high fertility, sub-Saharan Africa is projected to experience the fastest overall growth, rising from 12% of the world’s population in 2010 to about 20% in 2050. The Middle East-North Africa region also is expected to grow faster than the world as a whole, edging up from 5% of the global population in 2010 to 6% in 2050. Ongoing growth in both regions will fuel global increases in the Muslim population. In addition, sub-Saharan Africa’s Christian population is expected to double, from 517 million in 2010 to 1.1 billion in 2050. The share of the world’s Christians living in sub-Saharan Africa will rise from 24% in 2010 to 38% in 2050.

Meanwhile, the Asia-Pacific region is expected to have a declining share of the world’s population (53% in 2050, compared with 59% in 2010). This will be reflected in the slower growth of religions heavily concentrated in the region, including Buddhism and Chinese folk religions, as well as slower growth of Asia’s large unaffiliated population. One exception is Hindus, who are overwhelmingly concentrated in India, where the population is younger and fertility rates are higher than in China or Japan. As previously mentioned, Hindus are projected to roughly keep pace with global population growth. India’s large Muslim population also is poised for rapid growth. Although India will continue to have a Hindu majority, by 2050 it is projected to have the world’s largest Muslim population, surpassing Indonesia.

The remaining geographic regions also will contain declining shares of the world’s population: Europe is projected to go from 11% to 8%, Latin American and the Caribbean from 9% to 8%, and North America from 5% to a little less than 5%.

Europe is the only region where the total population is projected to decline. Europe’s Christian population is expected to shrink by about 100 million people in the coming decades, dropping from 553 million to 454 million. While Christians will remain the largest religious group in Europe, they are projected to drop from three-quarters of the population to less than two-thirds. By 2050, nearly a quarter of Europeans (23%) are expected to have no religious affiliation, and Muslims will make up about 10% of the region’s population, up from 5.9% in 2010. Over the same period, the number of Hindus in Europe is expected to roughly double, from a little under 1.4 million (0.2% of Europe’s population) to nearly 2.7 million (o.4%), mainly as a result of immigration. Buddhists appear headed for similarly rapid growth in Europe – a projected rise from 1.4 million to 2.5 million.

In North America, Muslims and followers of “other religions” are the fastest-growing religious groups. In the United States, for example, the share of the population that belongs to other religions is projected to more than double – albeit from a very small base – rising from 0.6% to 1.5%.9Christians are projected to decline from 78% of the U.S. population in 2010 to 66% in 2050, while the unaffiliated are expected to rise from 16% to 26%. And by the middle of the 21st century, the United States is likely to have more Muslims (2.1% of the population) than people who identify with the Jewish faith (1.4%).10

In Latin America and the Caribbean, Christians will remain the largest religious group, making up 89% of the population in 2050, down slightly from 90% in 2010. Latin America’s religiously unaffiliated population is projected to grow both in absolute number and percentage terms, rising from about 45 million people (8%) in 2010 to 65 million (9%) in 2050.11

Changing Religious Majorities

Several countries are projected to have a different religious majority in 2050 than they did in 2010. The number of countries with Christian majorities is expected to decline from 159 to 151, as Christians are projected to drop below 50% of the population in Australia, Benin, Bosnia-Herzegovina, France, the Netherlands, New Zealand, the Republic of Macedonia and the United Kingdom.

Muslims in 2050 are expected to make up more than 50% of the population in 51 countries, two more than in 2010, as both the Republic of Macedonia and Nigeria are projected to gain Muslim majorities. But Nigeria also will continue to have a very large Christian population. Indeed, Nigeria is projected to have the third-largest Christian population in the world by 2050, after the United States and Brazil.

As of 2050, the largest religious group in France, New Zealand and the Netherlands is expected to be the unaffiliated.

About These Projections

While many people have offered predictions about the future of religion, these are the first formal demographic projections using data on age, fertility, mortality, migration and religious switching for multiple religious groups around the world. Demographers at the Pew Research Center in Washington, D.C., and the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria, gathered the input data from more than 2,500 censuses, surveys and population registers, an effort that has taken six years and will continue.

The projections cover eight major groups: Buddhists, Christians, Hindus, Jews, Muslims, adherents of folk religions, adherents of other religions and the unaffiliated (see Appendix C: Defining the Religious Groups). Because censuses and surveys in many countries do not provide information on religious subgroups – such as Sunni and Shia Muslims or Catholic, Protestant and Orthodox Christians – the projections are for each religious group as a whole. Data on subgroups of the unaffiliated are also unavailable in many countries. As a result, separate projections are not possible for atheists or agnostics.

The projection model was developed in collaboration with researchers in the Age and Cohort Change Project at IIASA, who are world leaders in population projections methodology. The model uses an advanced version of the cohort-component method typically employed by demographers to forecast population growth. It starts with a population of baseline age groups, or cohorts, divided by sex and religion. Each cohort is projected into the future by adding likely gains (immigrants and people switching in) and by subtracting likely losses (deaths, emigrants and people switching out) year by year. The youngest cohorts, ages 0-4, are created by applying age-specific fertility rates to each female cohort in the childbearing years (ages 15-49), with children inheriting the mother’s religion. For more details, see the Methodology.12

In the process of gathering input data and developing the projection model, the Pew Research Center previously published reports on the current size and geographic distribution of major religious groups, including Muslims (2009), Christians (2011) andseveral other faiths (2012). An initial set of projections for one religious group, Muslims, was published in 2011, although it did not attempt to take religious switching into account.

Some social theorists have suggested that as countries develop economically, more of their inhabitants will move away from religious affiliation. While that has been the general experience in some parts of the world, notably Europe, it is not yet clear whether it is a universal pattern.13 In any case, the projections in this report are not based on theories about economic development leading to secularization.

Rather, the projections extend the recently observed patterns of religious switching in all countries for which sufficient data are available (70 countries in all). In addition, the projections reflect the United Nations’ expectation that in countries with high fertility rates, those rates gradually will decline in coming decades, alongside rising female educational attainment. And the projections assume that people gradually are living longer in most countries. These and other key input data and assumptions are explained in detail in Chapter 1 and the Methodology (Appendix A).

Since religious change has never previously been projected on this scale, some cautionary words are in order. Population projections are estimates built on current population data and assumptions about demographic trends, such as declining birth rates and rising life expectancies in particular countries. The projections are what will occur if the current data are accurate and current trends continue. But many events – scientific discoveries, armed conflicts, social movements, political upheavals, natural disasters and changing economic conditions, to name just a few – can shift demographic trends in unforeseen ways. That is why the projections are limited to a 40-year time frame, and subsequent chapters of this report try to give a sense of how much difference it could make if key assumptions were different.

For example, China’s 1.3 billion people (as of 2010) loom very large in global trends. At present, about 5% of China’s population is estimated to be Christian, and more than 50% is religiously unaffiliated. Because reliable figures on religious switching in China are not available, the projections do not contain any forecast for conversions in the world’s most populous country. But if Christianity expands in China in the decades to come – as some experts predict – then by 2050, the global numbers of Christians may be higher than projected, and the decline in the percentage of the world’s population that is religiously unaffiliated may be even sharper. (For more details on the possible impact of religious switching in China, see Chapter 1.)

Finally, readers should bear in mind that within every major religious group, there is a spectrum of belief and practice. The projections are based on the number of people whoself-identify with each religious group, regardless of their level of observance. What it means to be Christian, Muslim, Hindu, Buddhist, Jewish or a member of any other faith may vary from person to person, country to country, and decade to decade.

Acknowledgements

These population projections were produced by the Pew Research Center as part of the Pew-Templeton Global Religious Futures project, which analyzes religious change and its impact on societies around the world. Funding for the Global Religious Futures project comes from The Pew Charitable Trusts and the John Templeton Foundation.

Many staff members in the Pew Research Center’s Religion & Public Life project contributed to this effort. Conrad Hackett was the lead researcher and primary author of this report. Alan Cooperman served as lead editor. Anne Shi and Juan Carlos Esparza Ochoa made major contributions to data collection, storage and analysis. Bill Webster created the graphics and Stacy Rosenberg and Ben Wormald oversaw development of the interactive data presentations and the Global Religious Futures website. Sandra Stencel, Greg Smith, Michael Lipka and Aleksandra Sandstrom provided editorial assistance. The report was number-checked by Shi, Esparza Ochoa, Claire Gecewicz and Angelina Theodorou.

Several researchers in the Age and Cohort Change project of the International Institute for Applied Systems Analysis collaborated on the projections, providing invaluable expertise on advanced (“multistate”) population modeling and standardization of input data. Marcin Stonawski wrote the cutting-edge software used for these projections and led the collection and analysis of European data. Michaela Potančoková standardized the fertility data. Vegard Skirbekk coordinated IIASA’s research contributions. Additionally, Guy Abel at the Vienna Institute of Demography helped construct the country-level migration flow data used in the projections.

Over the past six years, a number of former Pew Research Center staff members also played critical roles in producing the population projections. Phillip Connor prepared the migration input data, wrote descriptions of migration results and methods, and helped write the chapters on each religious group and geographic region. Noble Kuriakose was involved in nearly all stages of the project and helped draft the chapter on demographic factors and the Methodology. Former intern Joseph Naylor helped design maps, and David McClendon, another former intern, helped research global patterns of religious switching. The original concept for this study was developed by Luis Lugo, former director of the Pew Research Center’s Religion & Public Life project, with assistance from former senior researcher Brian J. Grim and visiting senior research fellow Mehtab Karim.

Others at the Pew Research Center who provided editorial or research guidance include Michael Dimock, Claudia Deane, Scott Keeter, Jeffrey S. Passel and D’Vera Cohn. Communications support was provided by Katherine Ritchey and Russ Oates.

We also received very helpful advice and feedback on portions of this report from Nicholas Eberstadt, Henry Wendt Scholar in Political Economy, American Enterprise Institute; Roger Finke, Director of the Association of Religion Data Archives and Distinguished Professor of Sociology and Religious Studies, The Pennsylvania State University; Carl Haub, Senior Demographer, Population Reference Bureau; Todd Johnson, Associate Professor of Global Christianity and Director of the Center for the Study of Global Christianity, Gordon Conwell Theological Seminary; Ariela Keysar, Associate Research Professor and Associate Director of the Institute for the Study of Secularism in Society and Culture, Trinity College; Chaeyoon Lim, Associate Professor of Sociology, University of Wisconsin-Madison; Arland Thornton, Research Professor in the Population Studies Center, University of Michigan; Jenny Trinitapoli, Assistant Professor of Sociology, Demography and Religious Studies, The Pennsylvania State University; David Voas, Professor of Population Studies and Acting Director of the Institute for Social and Economic Research, University of Essex; Robert Wuthnow, Andlinger Professor of Sociology and Director of the Center for the Study of Religion, Princeton University; and Fenggang Yang, Professor of Sociology and Director of the Center on Religion and Chinese Society, Purdue University.

While the data collection and projection methodology were guided by our consultants and advisers, the Pew Research Center is solely responsible for the interpretation and reporting of the data.

Roadmap to the Report

The remainder of this report details the projections from multiple angles. The first chapter looks at the demographic factors that shape the projections, including sections on fertility rates, life expectancy, age structure, religious switching and migration. The next chapter details projections by religious group, with separate sections on Christians, Muslims, the religiously unaffiliated, Hindus, Buddhists, adherents of folk or traditional religions, members of “other religions” (consolidated into a single group) and Jews. A final chapter takes a region-by-region look at the projections, including separate sections on Asia and the Pacific, Europe, Latin America and the Caribbean, the Middle East and North Africa, North America and sub-Saharan Africa.

1. This overall projection (9.3 billion in 2050) matches the “medium variant” forecast in the United Nations Population Division’s World Population Prospects, 2010 revision. A recent update from the United Nations has a somewhat higher estimate, 9.55 billion. The U.N. does not make projections for religious groups. ↩
2. Christianity began about six centuries before Islam, a head start that helps explain why some scholars believe that, in the past, Christians always have been more numerous than Muslims around the world. The Pew Research Center consulted several scholars on this historical question. Todd M. Johnson, co-editor of the “Atlas of Global Christianity,” and Houssain Kettani, author of independent estimates of the growth of Islam, contend that the number of Christians always has exceeded the number of Muslims. But some other experts, including Oxford University demographer David Coleman and Columbia University historian Richard W. Bulliet, say it is possible that Muslims may have outnumbered Christians globally sometime between 1000 and 1600 C.E., as Muslim populations expanded and Christian populations were decimated by the Black Death in Europe. All of the experts acknowledged that estimates of the size of religious groups in the Middle Ages are fraught with uncertainty. ↩
3. Although some faiths in the “other religions” category have millions of adherents around the world, censuses and surveys in many countries do not measure them specifically. Because of the scarcity of census and survey data, Pew Research has not projected the size of individual religions within this category. Estimates of the global size of these faiths generally come from other sources, such as the religious groups themselves. By far the largest of these groups is Sikhs, who numbered about 25 million in 2010, according to the World Religion Database. Estimates from other sources on the size of additional groups in this category can be found in the sidebar in Chapter 2. ↩
4. Jews make up such a small share of the global population, however, that the projected decline is not visible when percentages are rounded to one decimal place. Jews comprised 0.20% of the world’s population in 2010 and are projected to comprise 0.17% in 2050. Both figures are rounded to 0.2% (two-tenths of 1%) in the charts and tables in this report. ↩
5. In many countries, censuses and demographic surveys do not enumerate atheists and agnostics as distinct populations, so it is not possible to reliably estimate the global size of these subgroups within the broad category of the religiously unaffiliated. ↩
6. The standard measure of fertility in this report is the Total Fertility Rate. In countries with low infant and child mortality rates, a Total Fertility Rate close to 2.1 children per woman is sufficient for each generation to replace itself. Replacement-level fertility is higher in countries with elevated mortality rates. For more information on how fertility shapes population growth, see Chapter 1. ↩
7. Most immigrants come to GCC countries as temporary workers. These projections model a dynamic migrant population in GCC countries, in which some migrants leave as others arrive and, over time, there are net gains in the size of the foreign-born population within each GCC country. ↩
8. The assumptions and trends used in these projections are discussed in Chapter 1 and in the Methodology section (Appendix A). ↩
9. As noted above, the “other religions” category includes many groups – such as Baha’is, Sikhs and Wiccans – that cannot be projected separately due to lack of data on their fertility rates, age structure and other demographic characteristics.↩
10. People who identify their religion as Jewish in surveys are projected to decline from an estimated 1.8% of the U.S. population in 2010 to 1.4% in 2050. These figures, however, do not include “cultural” or “ethnic” Jews – people who have Jewish ancestry but do not describe their present religion as Jewish. A 2013 Pew Research survey found that more than one-in-five U.S. Jewish adults (22%) say they are atheist, agnostic or nothing in particular, but consider themselves Jewish aside from religion and have at least one Jewish parent. For the purposes of the religious group projections in this report, people who identify their religion as atheist, agnostic or nothing in particular are categorized as unaffiliated. To avoid double-counting, they are not included in the Jewish population. If the projected Jewish numbers were expanded to include cultural or ethnic Jews, it is possible that the size of the more broadly defined Jewish population might be greater than the projected number of U.S. Muslims in 2050. ↩
11. The global projections are for Christians as a whole and do not attempt to calculate separate growth trajectories for subgroups such as Catholics and Protestants. However, other studies by the Pew Research Center show that Catholics have been declining and Protestants have been rising as a percentage of the population in some Latin American countries. See the Pew Research Center’s 2014 report “Religion in Latin America.” ↩
12. How accurate have population projections using the cohort-component method been in the past? An overview of how previous projections for general populations compare with actual population trends is provided in the National Research Council’s 2000 book “Beyond Six Billion: Forecasting the World’s Population,”http://www.nap.edu/catalog/9828/beyond-six-billion-forecasting-the-worlds- population. ↩
13. For example, there is little evidence of economic development leading to religious disaffiliation in Muslim-majority countries. In Hindu-majority India, religious affiliation remains nearly universal despite rapid social and economic change. And in China, religious affiliation – though very difficult to measure – may be rising along with economic development. ↩