I forgot to add that to compare several very unevenly distributed denominations and call one of them more evenly spread than the others is a statistically nonsensical way of phrasing things. Instead, it would be more helpful to state the following:
"While no denomination has an "even" spread of membership (i.e., defined as similar ratio of members to population in all countries) in all countries of the world, one denomination has relatively less uneveness of spread, Jehovah's Witnesses." Then it would be a matter of demonstrating the accuracy of this assertion by JW-memberships across different countries with other denominations. Let the comparisions begin if those sorts of membership/population ratio membership figures are available for various denominations.