Income Requirements for Tenant Criteria

[Mike Healey]

I am in the process of going through the tenant application/screening process for the first time. Currently I'm writing up some selection criteria and came across a question on income requirements. I went with the standard 3x gross monthly income. 

How does this work if you have two people looking to occupy a unit? Do they both need to meet this standard individually? Or can you count their incomes together? If two people intend to occupy the unit, and neither of them meets the income requirement on their own, I suppose you run the risk of one of them moving out, leaving the other unable to make ends meet. Do you require a co-signer (a third party in this case) to sign?

Just curious how others handle it.