Here is some info from JWFACTS.com
" In 1969 there was one baptism for every 1,983 hours of preaching. During the 1980s it had risen to 3,000 hours. From 1990 to 2005 the number of hours preaching required per baptism increased from 3000 to 5000, an increase of 60%.
More significant is the number of hours required for an additional publisher. Due to the large increase in Witnesses leaving the religion, the number of hours preaching required per additional publisher has doubled from 4,000 in the early 1990's to over 8,000 since 2000. The difference from 1991 and 2005 from 4,000 to 16,000 is 400%."
Here is the page it was taken from, lots of great number crunching on that page.
http://www.jwfacts.com/watchtower/statistics.php
NJY