I don't know if this has been posted earlier.
I found some interesting figures on the JWs in the US, based on a research project - American Religious Identification Survey 2001 - by the City University of New York. The data are based on a telephone survey among 50,000 households. The basic question was 'what is your religion'? This was compared with data obtained from a similar survey conducted in 1990.
This sample gave the following results on the amount of JWs in the US. The figures between brackets are those published by the WTS)
1990: 1,381,000 (WTS yb 1991: 952,312)
2001: 1,331,000 (WTS yb 2002: 1,101,334)
(The WTS figures are highpoints plus pioneers)
Taking for granted that some of the difference between the CUNY and WTS data may be explained by sampling error, it's obvious that more people consider themselves JWs than as indicated by the Society. Further, it seems that the more than 15% increase in the 1990-2001 decade, as noted by the Society, might be questionable.
A second observation from the CUNY research was: "Some groups such as Mormons and Jehovah's Witnesses appear to attract a large number of converts ("in-switchers"), but also nearly as large a number of apostates ("out-switchers").
The complete report can be seen/downloaded at http://www.gc.cuny.edu/faculty/research_studies/aris.pdf - See particularly 'Exhibit 7