The demographics of atheism are difficult to quantify. Different people interpret "atheist" and related terms differently, and it can be hard to draw boundaries between atheism, non-religious beliefs, and non-theistic religious and spiritual beliefs. Furthermore, atheists may not report themselves as such, to prevent suffering from social stigma, discrimination, and persecution in certain regions, or in cases where the situation is reversed, religious people may keep their beliefs secret in societies with a pro-atheist government. Despite these problems, one study classified 2.5% of the world's population as atheists, and a separate 12.7% as non-religious.