The study of religiosity and intelligence explores the link between religiosity and intelligence or educational level (by country and on the individual level). Religiosity and intelligence are both complex topics that include diverse variables, and the interactions among those variables are not always well understood. For instance, intelligence is often defined differently by different researchers; also, all scores from intelligence tests are only estimates of intelligence, because one cannot achieve concrete measurements of intelligence (as one would of mass or distance) due to the concept’s abstract nature. Religiosity is also complex, in that it involves wide variations of interactions of religious beliefs, practices, behaviors, and affiliations, across a diverse array of cultures. A meta-analysis and an updated analysis by the same research group have found a measurable negative correlation between intelligence quotient (IQ) and religiosity. The correlation was suggested to be a result of nonconformity, more cognitive and less intuitive thinking styles among the less religious, and less of a need for religion as a coping mechanism. Another study showed a correlation between national average IQ and levels of atheism in society. However, other studies have questioned these explanations and correlations and have countered that any correlations are due to a complex range of social, economic, educational and historical factors, which interact with religion and IQ in different ways. Less developed and poorer countries tend to be more religious, perhaps because religions play a more active social, moral and cultural role in those countries. One study suggests that intuitive thinking may be one out of many sources that affect levels of religiosity and that analytical thinking may be one out of many sources that affect disbelief. However, others who have reviewed studies on analytic thinking and nonbelievers suggest that analytical thinking does not imply better reflection on religious matters or disbelief. A global study on educational attainment found that Jews, Christians, religiously unaffiliated persons, and Buddhists have, on average, higher levels of education than the global average. Numerous factors affect both educational attainment and religiosity. Definitions and issues Intelligence The definitions of intelligence are controversial since at least 70 definitions have been found among diverse fields of research. Some groups of psychologists have suggested the following definitions: From "Mainstream Science on Intelligence" (1994), an op-ed statement in the Wall Street Journal signed by fifty-two researchers (out of 131 total invited to sign). From "Intelligence: Knowns and Unknowns" (1995), a report