The Gallup poll has a broad question: the question “Is religion important in your daily life?” was asked; the “yes” and “no” answers are represented below. Discrepancies are due to the “Don’t Know” and “Refused” answers. In terms of demographics, India ranks as the country with the largest number of highly religious people in the world, with an estimated 960 million to 1 billion believers. China, although with less than a fifth of its total population (~18-19%), ranks second, with an estimated 240-250 million believers, followed by Indonesia, the United States, Brazil, and Nigeria.
via Importance of religion by country – Wikipedia, the free encyclopedia.
