"If you have 15 percent of the electorate refusing to say whom they’ll vote for, and if probably about half of the 27 percent in the “don’t know” category are in fact “soft” refusals who are similarly reluctant to reveal their preferences, those votes won’t necessarily have wound up in Mr. Mousavi’s column. If these Iranians were too intimidated to reveal their preferences to a pollster, they may also have been too intimidated to vote as they really pleased on Friday."
~ FiveThirtyEight: Politics Done Right: Polling Predicted Intimidation — and Not Necessarily Ahmadinejad’s Victory