I am not sure you are going to get a representative sample this way. Here is an interesting article. It is a little dated, but it might provide some food for thought.
Why the Jehovah’s Witnesses Grow so Rapidly: A Theoretical Application Journal of Contemporary Religion, Vol. 12, No. 2, 1997 by Rodney Stark and Laurence R. Iannaccone
Page 17
In order to succeed,
6. Religious movements must maintain a level of fertility sufficient to offset member mortality.
Many religious movements have been doomed, because they had such low levels of fertility that very high rates of conversion soon were necessary merely to offset high rates of mortality. No such problems confront the Witnesses. The Canadian Census reveals them to be slightly younger than Canadians in general. Table 7 shows the same is true in the United States—Witnesses are more likely to be under 30 and less likely to be over 65 than is the general population. Moreover, active American Witnesses are more apt to be married than is the general population, which is confirmed by the American National Survey of Religious Identification (ANSRI). They also are far more likely to have large families—about a third have four or more children. The ANSRI failed to ask adults how many children they had, but it did obtain complete data on the composition of the household, which allowed the calculation that the mean household size (3.4) of Jehovah’s Witnesses is exceeded only by Mormons (3.8) among major religious groups (the general population figure is 2.6). However, Witnesses are disproportionately female, less so among the active members, less so according to the ANSRI, and even less so in Canada (55% female). It is typical for religious movements to over-recruit women (Miller & Hoffman, 1995), but this is not important so long as it does not result in too little fertility. It is of interest that the Witnesses are about as likely as other Americans to have been divorced.
It has long been noticed that the Witnesses are very unusual for their degree of racial and ethnic integration, not only among the rank and file, but among leaders as well. Witness literature has always been quite militant in its stand against all forms of prejudice and discrimination. The data fully support these perceptions. Both the GSS data and the ANSRI data reveal that white, non- Hispanic Americans make up less than half of self-identified American Witnesses. African- Hispanic- and Asian-Americans form the majority. This may greatly facilitate the appeal of the movement in Latin America, Africa and parts of Asia.
