Demographics
It is difficult to quantify the number of atheists in the world. Respondents to religious-belief polls may define "atheism" differently or draw different distinctions between atheism, non-religious beliefs, and non-theistic religious and spiritual beliefs. A Hindu atheist would declare oneself as a Hindu, although also being an atheist at the same time. A 2005 survey published in Encyclopædia Britannica found that the non-religious made up about 11.9% of the world's population, and atheists about 2.3%. This figure did not include those who follow atheistic religions, such as some Buddhists. A broad figure estimates the number of atheists and agnostics on Earth at 1.1 billion.
A November–December 2006 poll published in the Financial Times gives rates for the United States and five European countries. The lowest rates of atheism were in the United States at only 4%, while the rates of atheism in the European countries surveyed were considerably higher: Italy (7%), Spain (11%), Great Britain (17%), Germany (20%), and France (32%). The European figures are similar to those of an official European Union survey, which reported that 18% of the EU population do not believe in a god. Other studies have placed the estimated percentage of atheists, agnostics, and other nonbelievers in a personal god as low as single digits in Poland, Romania, Cyprus, and some other European countries, and up to 85% in Sweden, 80% in Denmark, 72% in Norway, and 60% in Finland. According to the Australian Bureau of Statistics, 22% of Australians have "no religion", a category that includes atheists. Between 64% and 65% of Japanese and up to 81% of Vietnamese are atheists, agnostics, or do not believe in a god. A 2012 Gallup survey reported that 13% of people surveyed worldwide self-report to be atheists. In the United States, there was a 1% to 5% increase in self-reported atheism from 2005 to 2012, and a larger drop in those who self-identified as "religious", down by 13%, from 73% to 60%.
A study noted positive correlations between levels of education and secularity, including atheism, in America, and an EU survey found a positive correlation between leaving school early and believing in a God. A letter published in Nature in 1998 reported a survey suggesting that belief in a personal god or afterlife was at an all-time low among the members of the U.S. National Academy of Science, 7.0% of whom believed in a personal god as compared with more than 85% of the general U.S. population, although this study has been criticized by Rodney Stark and Roger Finke for its definition of belief in God. The definition was "I believe in a God to whom one may pray in the expectation of receiving an answer". An article published by The University of Chicago Chronicle that discussed the above study, stated that 76% of physicians believe in God, more than the 7% of scientists above, but still less than the 85% of the general population. Another study assessing religiosity among scientists who are members of the American Association for the Advancement of Science found that "just over half of scientists (51%) believe in some form of deity or higher power; specifically, 33% of scientists say they believe in God, while 18% believe in a universal spirit or higher power." Frank Sulloway of the Massachusetts Institute of Technology and Michael Shermer of California State University conducted a study which found in their polling sample of "credentialed" U.S. adults (12% had Ph.Ds and 62% were college graduates) 64% believed in God, and there was a correlation indicating that religious conviction diminished with education level. In 1958, Professor Michael Argyle of the University of Oxford analyzed seven research studies that had investigated correlation between attitude to religion and measured intelligence among school and college students from the U.S. Although a clear negative correlation was found, the analysis did not identify causality but noted that factors such as authoritarian family background and social class may also have played a part. Sociologist Philip Schwadel found that higher levels of education are associated with increased religious participation and religious practice in daily life, but also correlate with greater tolerance for atheists' public opposition to religion and greater skepticism of "exclusivist religious viewpoints and biblical literalism".
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