Juan Cole points to a new report from Chatham House that seeks to spell out the alleged rigging of the Iranian elections. The report is here (PDF) and the cover webpage here. Juan's analysis is here.
I'm no expert on statistics, but for those who've been asking where the evidence of fraud is, this may provide something of an answer. As I've said before, though, this has long since become an issue of perception rather than fact: virtually everyone outside Iran and increasing numbers inside are convinced the results were rigged, and the protests are likely to continue in any event.