But there's more to Erie than that, and the recent case, Hogan v. Novartis Pharmaceuticals, Inc., 06 Civ. 0260 (BMC) (RER), slip op. (E.D.N.Y. April 6, 2011), illustrates what else Erie entails. "Erie" is a shorthand for a famous U.S. Supreme Court case, Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), that established the modern framework for deciding what law governs - state or federal - in case removed from federal to state court under diversity jurisdiction.
At the risk of being almost misleadingly simplistic, Erie essentially says that the substantive rules of decision for diversity cases are governed by state law (that's why expansive interpretations of state law come under the doctrine), whereas "procedural" matters - especially those encompassed by the various federal rules of this or that - are governed by federal law.
Among the items designated as "procedural" are the Federal Rules of Evidence - or so the plaintiff in Hogan found out when she tried to argue otherwise. Like most prescription drug cases, Hogan involves failure to warn. It's a Zometa case, and after the plaintiff stopped using the drug, the FDA changed the label to toughen the relevant warnings.
As we've discussed before, a subsequent label change is a "subsequent remedial measure" - a post accident change intended to increase the safety of, here, the product at issue. For various reasons, chiefly not to deter defendants from making things safer, the prevailing rule is that subsequent remedial measures aren't admissible to prove that the defendant was negligent before, for not having done what it later did. The post-1997 version of Fed. R. Evid. 407 (the relevant federal rule) explicitly states that post-accident changes to a product are not evidence that earlier versions of the product was defective.
Hogan, however, comes from Rhode Island, where at some point in the past, the plaintiffs side hijacked the state's rules committee and produced a version of Rule 407 that's diametrically opposed to the federal (and almost every other state's) version. Rhode Island's rule expressly allows subsequent safety changes to be admissible into evidence. R.I. R. Evid 407 ("[w]hen, after an event, measures are taken which, if taken previously, would have made the event less likely to occur, evidence of the subsequent measures is admissible"). For technological advances and other safety improvements, Rhode Island is thus something of a stalag.
In Hogan, the plaintiff took a Sgt. Shultz attitude towards federal Erie practice - knowing nothing and seeing nothing. Fortunately the court shot her down. Essentially, for Erie purposes, a rule is a rule is a rule. If it's in the federal rules, then it controls in a diversity case removed to federal court:
Plaintiffs claim that the Rhode Island Rule must govern because it is substantive rather than procedural misses the mark. The inquiry begins and ends with the federal rule; Hanna teaches that if the federal rule is valid, the Court will apply it. To determine the rule's validity, the Court must ask what it regulates: If it governs only the manner and the means by which the litigants' rights are enforced, it is valid; if it alters the rules of decision by which the court will adjudicate those rights, it is not.Hogan, slip op. at 4-5 (quotation marks omitted). Needless to say, Hogan was not about to strike down Rule 407 as unconstitutional.
Thus, Hogan stands for two important principles. First, that subsequent label changes are excludable under Rule 407, and second, that in general in federal court a favorable federal rule will trump an unfavorable state rule on the same subject.