Here in the Third Circuit, including Pennsylvania, we do have some time frame with which to work. But, it's kept a little gray. As recognized by the Middle District of Pennsylvania earlier this year, a plaintiff can establish a causal connection by proving:
[A]n usually suggestive temporal proximity between the protected activity and the allegedly retaliatory action . . . . The Third Circuit has held that two days between a protected activity and an adverse action is "unusually suggestive" of retaliatory motive, but that three months is not. See Krouse v. Am. Sterlizer Co., 126 F.3d 494, 503 (3d Cir.1997); LeBoon v. Lancaster Jewish Cmty. Ctr. Ass'n, 503 F.3d 217, 233 (3d Cir.2007).Lease v. Fishel, 1:07-CV-0003, 2011 WL 381656 (M.D. Pa. Jan. 28, 2011). It's not hard science, but it does provide some guidance.
Note: I used Twitter Blackbird Pie to embed the tweet. I'd be interested to hear your feedback. I like that it's interactive (you can click Reply, Retweet, the usernames and it behaves as though you were in Twitter). It looks a little rough to me though (particularly the white boxes).
Posted by Philip Miles, an attorney with McQuaide Blasko in State College, Pennsylvania in the firm's civil litigation and labor and employment law practice groups.