The topic of religiosity and intelligence pertains to relationships between intelligence and religiosity, the extent to which someone is religious. Multiple studies have been undertaken to examine these relationships.
Intelligence is an umbrella term used to describe a property of the mind that encompasses many related abilities, such as the capacities to reason, to plan, to solve problems, to think abstractly, to comprehend ideas, to use language, and to learn. There are several ways to define intelligence. In some cases, intelligence may include traits such as creativity, personality, character, knowledge, or wisdom. However, some psychologists prefer not to include these traits in the definition of intelligence .
A widely-researched index or classification of intelligence among scientists is Intelligence Quotient (I.Q.). I.Q. is a summary index, calculated by testing individuals' abilities in a variety of tasks and producing a composite score to represent overall ability, e.g., Wechsler Adult Intelligence Scale. It is used to predict educational outcomes and other variables of interest.
Others have attempted to measure intelligence indirectly by looking at individuals' or group's educational attainment, although this risks bias from other demographic factors, such as age, income, gender and cultural background, all of which can affect educational attainment.
Dissatisfaction with traditional IQ tests has led to the development of alternative theories, all of which suggest that intelligence is the result of independent abilities that contribute to human performance. In 1983, Howard Gardner proposed the theory of multiple intelligences, which claims a broadening of the conventional definition of intelligence is needed, since, if intelligence is defined as the cognitive or mental capacity of an individual, this would logically include all forms of mental qualities, not simply the ones most transparent to standardized I.Q. tests. The categories of intelligences Gardner proposes are logical, linguistic, spatial, musical, kinesthetic, naturalist, intrapersonal and interpersonal intelligences.
Jean Piaget developed stages as an alternative to IQ after studying the nature of the wrong answers on items. The Model of hierarchical complexity was formed as an alternative to IQ. Performance on the items varying in hierarchical complexity from 0 to 14, is absolute, and does not require norms. Because the orders are content and context free, they can be used to measure performance in any domain, including the ones mention by Gardner and Goleman.
Religiosity is a sociological term referring to degrees of religious behaviour, belief or spirituality. The measurement of religiosity is hampered by the difficulties involved in defining what is meant by the term. Numerous studies have explored the different components of religiosity, with most finding some distinction between religious beliefs/ doctrine, religious practice, and spirituality. Studies can measure religious practice by counting attendance at religious services, religious beliefs/ doctrine by asking a few doctrinal questions, while spirituality can be measured by asking respondents about their sense of oneness with the divine or through detailed standardized measurements. When religiosity is measured, it is important to specify which aspects of religiosity are referred to.
In 2008, intelligence researcher Helmuth Nyborg examined whether IQ relates to denomination and income, using representative data from the National Longitudinal Study of Youth, which includes intelligence tests on a representative selection of American youth, where they have also replied to questions about religious belief. His results, published in the scientific journal Intelligence demonstrated that on average, Atheists scored 1.95 IQ points higher than Agnostics, 3.82 points higher than Liberal persuasions, and 5.89 IQ points higher than Dogmatic persuasions.  "I'm not saying that believing in God makes you dumber. My hypothesis is that people with a low intelligence are more easily drawn toward religions, which give answers that are certain, while people with a high intelligence are more skeptical," says the professor.
Nyborg also co-authored a study with Richard Lynn, emeritus professor of psychology at the University of Ulster, which compared religious belief and average national IQs in 137 countries.  The study analysed the issue from several viewpoints. Firstly, using data from a U.S. study of 6,825 adolescents, the authors found that atheists scored 6 g-IQ points higher than those adhering to a religion.
Secondly, the authors investigated the link between religiosity and intelligence on a country level. Among the sample of 137 countries, only 23 (17%) had more than 20% of atheists, which constituted “virtually all the higher IQ countries.” The authors reported a correlation of 0.60 between atheism rates and level of intelligence, which is “highly statistically significant.” This portion of the study uses the same data set as Lynn's work IQ and the Wealth of Nations.
Commenting on the study in The Daily Telegraph, Lynn said "Why should fewer academics believe in God than the general population? I believe it is simply a matter of the IQ. Academics have higher IQs than the general population. Several Gallup poll studies of the general population have shown that those with higher IQs tend not to believe in God," 
A small 2004 study by Ellen Paek empirically examined the extent to which religiosity, operationalized as religious orientation and religious behaviour, is related to Emotional Intelligence. Paek surveyed 148 church-attending adult Christians and found that religious orientation was positively correlated with overall EI and its subcomponent emotional understanding. While the number of religious group activities was positively associated with EI, years of church attendance was unrelated. Significant positive correlations were also found between level of religious commitment and EI. Both attitudinal and behavioral measures of religiosity were significant predictors of EI, particularly the former.
In their 2002 article, entitled “Linking emotional intelligence, spirituality and workplace performance: Definitions, models and ideas for research”, Tischler, Biberman and McKeage (2002) reviewed literature on both EI and various aspect of spirituality and found that both appear to lead to similar attitudes, behaviours and skills, and that there often seems to be confusion, intersection and linking between the two constructs. 
In 1975, Norman Poythress studied a sample of 234 US college undergraduates, grouping them into relatively homogeneous religious types based on the similarity of their religious beliefs, and compared their personality characteristics. He found that "Literally-oriented religious Believers did not differ significantly from Mythologically-oriented Believers on measures of intelligence, authoritarianism, or racial prejudice. Religious Believers as a group were found to be significantly less intelligent and more authoritarian than religious Skeptics." He used SAT's as a measure of intelligence for this study.
In the US, according to raw data from the 2004 General Social Survey, those with graduate degrees were the least likely to believe in the afterlife or the Bible as the word of God, suggesting a link between religious belief and lower educational attainment. 
A weak negative correlation between education and Christian fundamentalism was found by Burton et al. (1989), a small study comparing the religious beliefs and educational achievements of white, Protestant residents of Delaware County, Indiana. Contrary to the researchers' expectations, fundamentalist converts were not less educated people.
In Australia, 23% of Christian church attenders have earned a university or postgraduate degree, whereas the figure for the general population is 13%. Christianity is the predominant religion in Australia, although adherence is falling. Commentators on the Survey attribute the educational levels to sociological factors, such as age, class and income, making no claims about intelligence. 
Studies of Mormons in the US also display a high positive correlation between education levels and religiosity. Survey research indicated that 41% of Mormons with only elementary school education attend church regularly. By contrast, 76% of Mormon college graduates attend church regularly and 78% of Mormons who went beyond their college degrees to do graduate study attend church regularly.