outcome-determinative test

the intent of that decision was to insure that, in all cases where a federal court is exercising jurisdiction solely because of the diversity of citizenship of the parties, the outcome of the litigation in the federal court should be substantially the same, so far as legal rules determine the outcome of a litigation, as it would be if tried in a State court. The nub of the policy that underlies Erie R. Co. v. Tompkins is that for the same transaction the accident of a suit by a non-resident litigant in a federal court instead of in a State court a block away, should not lead to a substantially different result.