The Country Similarity Index attempts to quantify how similar countries are to each other relative to other countries. The index is a statistically-based way to measure this. 20% of the index is based on culture. 12.5% of a country’s culture score (2.5% of the overall Country Similarity Index score) is allocated for the typical religious beliefs of its people. The following is an explanation on how they were calculated:
(Note that religious beliefs in the culture category includes atheism or agnostic beliefs, unlike in the demographics section, which does not take atheism into account)
Religious Origins
The vast majority of people in the world follow a religion that originated from two major origins. Christianity, Islam, and Judaism are all monotheistic religions that essentially came from a similar tradition in the Middle East. These are known as Abrahamic religions. These religions now dominate Europe, Australia, Africa, and the Americas. Dharmic religions include both Hinduism and Buddhism. They are polytheistic and originated in India, but also spread to Southeast and East Asia. Eastern Religions like Taoism, Shintoism, and Confucianism are also prevalent in the Sinosphere. Another less widely disbursed branch of religions originate in Africa. These animistic folk religions most notably include Voodoo and are most prevalent in Benin and Togo.
The CIA Factbook and Wikipedia are the main sources of the data:
https://www.indexmundi.com/factbook/fields/religions
https://en.wikipedia.org/wiki/Importance_of_religion_by_country
Religion
The world’s major religions include Christianity, Islam, Buddhism, Hinduism, and Eastern Folk religions. Christianity is dominant in Europe, Australia, the Western Hemisphere, and Southern Africa. Islam is most common in the Middle East, North Africa, Turkic countries, Pakistan, Bangladesh, Malaysia, and Indonesia. Buddhism is practiced most widely in Southeast Asia, but also in East Asia and Sri Lanka. Hinduism, despite having many adherents, only has a majority in India and Nepal, but it also has a significant following among the Indian diaspora throughout the world. This category also factors in the amount of irreligious people in a country. Czech Republic is one of the least religious countries in the world. In general, Northern Europe, Eastern Europe, and East Asia have the largest percentage of irreligious people. This is in part because many of these countries had governments controlled by the Communist Party, which discouraged religion.
The CIA Factbook and Wikipedia are the main sources of the data:
https://www.indexmundi.com/factbook/fields/religions
https://en.wikipedia.org/wiki/Importance_of_religion_by_country
Religious Denomination
Christianity has four major branches: Catholic, Protestant, Oriental Orthodox, and Eastern Orthodox. Catholicism is common in Southern Europe. It was also spread throughout Latin America by Spain, France, and Portugal. Protestantism is common in Northern Europe, which split from Catholicism during the reformation, beginning in the 16th century. It was also spread to many British colonies. The Oriental Orthodox and Eastern Orthodox denominations broke off from the Catholic church even earlier. The Eastern Orthodox denomination is most concentrated in Eastern Europe. The Oriental Orthodox church is by far the smallest branch. It is the major denomination in only three countries: Armenia, Ethiopia, and Eritrea. Muslims are also split into several major groups including Sunnis, Shi’ites, and Ibadis. The vast majority of Muslims are Sunnis. Iran and Azerbaijan are two countries that have a majority Shi’ite population, but it is also common in Iraq and Yemen. Ibadis are only common in Oman. Buddhism also has three major schools: Mahayana, Theravada, and Vajrayana. The Mahayana school is most common in East Asia and Vietnam. The Theravada school is concentrated in Southeast Asia and Sri Lanka. The Vajrayana school is the smallest. It is most common in Tibet, Bhutan, and Mongolia.
The CIA Factbook and Wikipedia are the main sources of the data:
https://www.indexmundi.com/factbook/fields/religions
https://en.wikipedia.org/wiki/Importance_of_religion_by_country
Calculation Method
The religions of two different countries are compared using the following method:
Example: Germany is 53% Christian, 6% Muslim, and 37% irreligious, therefore it gets 5 Christian points, 1 Muslim point, and 4 irreligious points. Brazil is 87% Christian, 0.2% Muslim, and 8% irreligious, therefore it gets 9 Christian points, 0 Muslim points, and 1 irreligious points. When religion in Germany and Brazil is compared, they receive credit for 5 points for Christians and 1 point for irreligious people, adding up to a total of 6 points out of 10 similarity points.