In 1997the most recent year for which global statistics are currently availablethe Church had an overall increase in membership of over ten million, only a little more than half of which can be accounted for by baptisms under the age of seven, and an increase in spite of the loss of members due to death and defection.
And the Catholic Church is growing not only in the world at large but in America in particular. In 1998the most recent year for which national statistics are availablethe U.S. Catholic population had an overall increase of 455,000, including 162,000 conversions to the Catholic Church (i.e., cases of people joining other than baptisms of those below the age of seven).
Catholic growth rates in both the United States and the world dwarf what any other church is doing. Nobody else in the world gets an net increase of ten million people in a year, and nobody else in America gets a net increase of half a million people in a year.
Even if we look at just U.S. membership growth without infant baptism, nobody else in America gets 162,000 new non-infant members in a year, nor does any other American church have an overall increase of half a million members a year.
Growth rates are no indication of truth, and religious affiliation should be based on truth. This is really the bottom line. It doesn't matter how many adherents a religion has.