A new report (pdf), "Beliefs About God Across Time And Countries," takes a global look at the question. Waldman pores over the research:
[T]he variations are enormous. In the Philippines, 83.6 percent of people say, "I know God exists and I have no doubts about it." In Great Britain it's only 16.8 percent. Even among some similarly developed countries there can be a wide variation; 38.4 percent of Spanish people have no doubts about God, but only 15.5 percent of French people feel the same. One fascinating result comes from Japan, where only 4.3 percent have no doubts about the existence of God, but only 8.7 percent say they don't believe in God at all. So almost nine out of ten Japanese are in the believing-ish category.