Well, to start, you can't compare an intervention (starting an ACE inhibitor treatment) to an existent factor (they already own a dog). If you're going to compa

Well, to start, you can't compare an intervention (starting an ACE inhibitor treatment) to an existent factor (they already own a dog). If you're going to compare apples to apples, you've got to compare starting an ACE inhibitor treatment to starting to own a dog. It may sound farfetched, but there's nothing in the OP that indicates the direction of causality to me, so it's possible that lower cardiovascular risk causes people to go out and get dogs, or that there's some root cause which causes people to both have lower cardiovascular risk and higher chance of owning a dog.