Consistent with the finding of the article described here, this article describes a Bloomberg study finding that backdating “has so far cost investors at least $7.9 billion in market value.” The analysis looks to have controlled for industry specific factors by comparing returns to applicable sector indexes. What’s not clear, and this is a point made by Steven Donegal in a comment to the post linked above, is how long the effects of backdating persist. The article notes that for some companies “the damage proved fleeting.” The article also points out that the impact on share price of a backdating revelation may be decreasing. “The average one-day loss for the first 30 companies to disclose investigations, from March 14 to May 25, was 2.9 percent, or 2.8 percentage points worse than their peers. The last 30 disclosures as of Aug. 31 prompted an average decline of 1 percent, trailing peers by 1.2 percentage points.”