I am an empiricist, so I always appreciate something more than anecdotes to make a case for something.
That said, even if the data do point to an uptick in new member activity following a broadcast, all this demonstrates is correlation, not causation. The correlation can be due to any number of reasons, including the most likely reason, in that a broadcast simply raises one's awareness of what is wrong with the organization, and encourages them to post. Very likely these people are already mentally out, and simply overcoming any fears or apprehensions to post.
It is all good though. The org. is doing more to destroy itself than any "apostate" ever could...
d4g