The Chicken or The Egg

I have been watching the statistics roll through about clergy health. The articles linked come from a variety of sources, and some different studies. Much of the latest turmoil seems to stem from The Clergy Health Initiative from Duke University - probably because it hits home with United Methodists in a new way.

One of the items I have not seen detail for is which came first, the chicken or the egg... put differently:

The cynic in me is beginning to wonder at the statistics we keep seeing. As a clergy person I am still concerned. I wonder how many of the conditions were pre-existing when someone came into ministry. The one that triggered that thought for me was the "asthma" question. I was diagnosed at 6 months, so I can't even say it was a product of my calling (which I heard at about 6 years old).
Are sick people more likely to fill a call to ministry, where they feel the "limitations" will be less obvious, or problematic, than other fields?
Peace,