This article compares the growth of three religious groups, the Church of Jesus Christ of Latter-day Saints, Seventh-day Adventists, and Jehovah’s Witnesses. All originated in America during the nineteenth century and have since globalized. It begins by using their official membership data to contrast their aggregate growth over time. It then questions the reliability of those official statistics. Noting that each group employs different criteria in selecting who it counts, it employs census data from 54 countries in all regions of the world and five surveys of US adult religious affiliation with adjustments for children as a proxy for an American census to provide a common basis for comparison. It finds consistent patterns, where membership data greatly overstate the number of Mormons, understate the number of Adventists, and also understate the number of Witnesses to an even greater extent. The article then calculates a weighted ratio between official and census data for each group and uses those ratios to estimate their aggregate adherents. This method results in a dramatic reordering of their sizes. Finally, the article accounts for the variations found between the three groups.
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