Bahá'í statistics

The Bahá'í World News Service reports a Bahá'í membership of more than 5 million worldwide, in "virtually every country" and many territories. Other sources such as Encyclopædia Britannica or the World Christian Encyclopedia have listed Bahá'í membership as over 7 million. The Bahá'í Faith is recognized as the second-most geographically widespread religion after Christianity, and the only religion to have grown faster than the population of the world in all major areas over the last century.

Membership data on a relatively new, worldwide religion are difficult to arrive at. The religion is almost entirely contained in a single, organised community, but the Bahá'í population is spread out and not in a majority anywhere. Populations are not assigned a Bahá'í religious adherence by birth, as is the case with other major religions such as Islam and Christianity. Few religious surveys include the Bahá'í Faith due to the high sample size required to reduce the margin of error, and those that have included the Bahá'í Faith are known to underestimate or overinflate many proportionally small groups. Additionally, Bahá'í membership data does not break out active participation from the total number of people who have expressed their belief.

The official claim of "more than five million Bahá’ís" in the world came originally in 1991 and hasn't changed since. The official agencies of the religion have focused on publishing more concrete data, such as numbers of local and national spiritual assemblies, countries and territories represented, languages and tribes represented, and publishing trusts.

In the 1930s the Bahá'ís of the United States and Canada began requiring new adherents to sign a declaration of faith, stating their belief in Bahá'u'lláh, the Báb, and `Abdu'l-Bahá, and an understanding that there are laws and institutions to obey. The original purpose of signing a declaration card was to allow followers to apply for lawful exemption from active military service. The signature of a card later became optional in Canada, but in the US is still used for records and administrative requirements. Many countries follow the pattern of the US and Canada.

Other than signing a card and being acknowledged by a Spiritual Assembly, there is no initiation or requirement of attendance to remain on the official roll sheets. Members receive regular mailings unless they request not to be contacted.

The fact that the religion is diffuse and proportionally small are major barriers to demographic research by outsiders. Even in the United States, where significant resources are dedicated to gathering data, the Bahá'í Faith is often left off of religious surveys due to the high sample size required to reduce the margin of error. In some countries the Bahá'í Faith is illegal and Bahá'ís endure some degree of persecution, making it difficult for even Bahá'ís to maintain a count.

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