Study shows large majority of world's population is religious

With nearly 60 percent of the world's population living in the Asia-Pacific region, it follows that the highest concentrations of Hindus, Buddhists, folk religionists, other religions, unaffiliated and Muslims live in the region, according to the Pew study.

Christianity is the most evenly dispersed religion, with the highest concentrations in Europe (26 percent of all Christians live there), followed by Latin America and the Caribbean (24 percent) and sub-Saharan Africa (24 percent). Another 13 percent of all Christians live in Asia and the Pacific, with 12 percent in North America.

Christians make up barely more than 1 percent of the population in the Middle East/North Africa region, where the faith originated, Pew noted.

Christians are youngest in sub-Saharan Africa, where their median age is 19 years. The oldest median age for Christians is in Europe at 42 years.

Those dispersion and median age factors tell the story of Christianity over the past century as its growth has shifted south through missionary efforts and the secularization of Europe.

"One hundred years ago, 80 percent of the Christians were in Europe and North America," Johnson said. "Today, it's only 40 percent."