MDs: How do you make referrals?

When a patient asks for a referral—a podiatrist, say, or a dermatologist, for some special attention outside your sphere—how do you decide whose name to give?

Do doctors have reciprocal agreements—“I’ll refer to you if you refer to me”? (I notice they often have each other’s business cards on file, ready to hand out.)

Do they name people who are in some little group that they belong to?

Do they actually research fellow physicians and single out those with the best reputations and records?

Do they follow their colleagues’ recommendations?

Do they just go by whom they know personally?

Do they let the insurance companies tell them?