The first thing that a person does before becoming a Witness is study. Then they get baptized.
The real key is to watch the leading indicators. If Bible studies are down 33%, then baptisms will drop. They have.
If baptisms are down 51%, then the total head count will drop. It is.
One more thing. Every JW family reports a home bible study, whether they have one or not. In my congregation, most of the BSs that are reported are family studies. If you assume that there is one family study for every four persons, then the number of "outside" studies has plummeted from 31,000 to 11,000.