Joe Lenski, whose Edison Research has been the sole provider of exit polling to the U.S. television networks since 2003, recounts his experience conducting an exit poll for the Azerbaijan parliamentary elections in 2005. He sees some significant parallels between Azerbaijan and the election just held in Iran:
First, the [Azerbaijan] election and the voting itself, which seemed open and fair at the time, turned out to be mostly for show. Once the initial results in Azerbaijan showed opposition candidates winning in certain districts, the electoral commission took steps to make sure the official results matched what the government desired, which is probably what happened in Iran. Basically, the authorities were fine with an open and seemingly fair election as long as their guy won. Once that outcome became less certain, procedures were probably put in place to make sure the official results matched what the government desired. The fraud is probably not universal, but, as in Azerbaijan, concentrated in the areas where the opposition was doing better than expected. This would explain much of the statistical evidence showing Ahmadinejad doing well in the official vote returns from provinces and towns where the reformist candidates did well in the 2005 election.
He has much more. Read the whole thing.