history threats

Original Message -------- Subject: history threats Date: Wed, 25 Aug 2004 13:57:31 -0400 From: Diana Silver Reply-To: American Evaluation Association Discussion List To: EVALTALK@BAMA.UA.EDU

I am looking for cases I can cite in which evaluators of a program, using a quasi-experimental design, have noted history threats in attempting to assess the impact of a given program. The case I have is of an evaluation of the Bay Area Rapid Transit System (BART) that showed that highway traffic decreased in 1974 when BART's Transbay Tunnel was opened. External events -- history-- posed a threat to their findings, because the gasoline shortage and higher gas prices due to the Arab oil embargo occured at about the same time. I'm looking for additional such examples-- can anyone help?