Perhaps. I never considered revolvers and installment accounts being lumped together. If an installment account is present (open), almost by definition it needs to have a positive balance. I'm not sure why FICO would consider that as a negative thing when we know that the presence of an open installment loan is a good thing. I suppose you can always have too much of a good thing, so it's possible that too many installment loans in theory could adversely impact score. Addinging in revolvers to the equation, if they are indeed lumped together in terms of accounts with balances is another variable making it more difficult to test, as you suggested above.
