A demographic report from the Pew Research Center, a nonpartisan American research organization, tracking changes in the size of the world's major religious groups between 2010 and 2020, including the rise in the Muslim population share and the size of the religiously unaffiliated population. Pew's established methodology and reputation as a research institution place this at this atlas's middle tier, a reputable secondary source rather than peer reviewed academic scholarship in the strict sense. It is a strong source for global demographic trend figures, stated with whatever caveats Pew itself attaches, such as its own noted uncertainty around figures for China. It is not a source on the religious content or lived experience behind the numbers.