Credit Score - Evaluating a score?

[Shaun Palmer]

Does anyone have any good references on how to evaluate a credit score? I always run a score with an application and typically my criteria is 620 because that is usually the cutoff for a lender to offer a mortgage. However, lately it is getting more difficult to find a tenant with a score above 620. I am considering lowering my criteria but I first want to understand what a "score" means in common terms (i.e. If I reduce my criteria to say 570, what does that mean in terms of risk of someone not paying the rent?). I just what to evaluate risk with the credit score. Is this possible and does anyone have a good tool or reference?