But say you are right Leolaia and it does accurately give an indication that the dropout rate of Witnesses born in the faith is higher than for other groups - how do you personally square that with the concurrent finding that Witnesses are growing faster than most other religions? Do you think that is all down to their highly successful preaching?
Bear in mind that one finding compares the current adult population of JWs to the population of adults who had childhood affiliation with JWs, whereas the other compares different fractions within the population of adults who had childhood affiliation with JWs. This is an important difference between the two; the two findings pertain to different (but overlapping) populations. One omits the adults that were JWs at the time of childhood affiliation, and the other omits children that are affiliated in the current JW population.
The groups that show significant decreases (% of total population) between childhood and adult affiliation include those that do not depend on proselytism, such as Catholics (-7.5%), Anglicans/Episcopals (-0.3%), Jews (-0.1%), whereas those that show increases, such as Pentacostal (0.5%), Non-demoninational Protestant (3%), Muslim (0.1%), Jehovah's Witness (0.1%), etc., are those that do invest time and resources on proselytism. In these groups, the net gain hides the true rate of loss; this can easily be seen in the official JW statistics, which reveal a loss of a significant proportion of JWs when the present yearly total is compared with an earlier total + intervening baptisms. So the rate of conversion is already more successful than would be apparent from looking at the net gain. If they retained more members, the overall increase would have been greater. And if the losses are continually replenished by gains of converts, with the rate of gain greater than than the rate of loss, then certainly the current adult population of those raised as JWs (which is NOT the current JW adult population) could easily have only a minority still in the religion, with the current adult population of JWs (which is NOT the current adult population of those raised as JWs) being still larger than it was in the past. Bear in mind too that proselytism brings in not only adult converts but their children as well, thereby contributing to the rate of people raised and born in the religion. And a certain proportion of children raised as JWs never baptize or otherwise commit to the religion before adulthood, so these would contribute to the dropout rate as well.
Edit: BTW, that 2001 survey sounds very interesting....that could well be evidence that the bias can go the other way.