For anyone trying to rig an election, technology is a mixed blessing. It certainly makes some things easier: you only need to change some figures on some centrally-located spreadsheets, instead of manually altering lots of locally-produced tallies and suborning hordes of minor officials. But it also makes it much easier to get caught.

So for the last week, while the Iranian regime has been fighting for survival on the streets of Tehran, it has also been fighting — and losing — a battle for world opinion on the credibility of its election results.

Supreme leader Ali Khamenei made his pitch last Friday: “There is 11 million votes difference,” the ayatollah said. “How can one rig 11 million votes?”

But in a centralised, relatively opaque system like Iran’s, the answer is “quite easily”. On Sunday, Chatham House, one of the world’s most prestigious think-tanks, released a particularly damning report, which, using the Iranian interior ministry’s own statistics, found a range of anomalies that are difficult to explain by anything other than fraud.

Among them was the fact that in a number of jurisdictions, including two whole provinces, the recorded turnout exceeded 100%. That’s not always a fatal objection; it would be in Australia, where rolls are compiled in advance and you have to be on the roll to vote, but in many countries the eligible voting population is only an estimate. Moreover, not everyone votes in their home city or even province.

Hence a spokesman for Iran’s guardian council, Abbas-Ali Kadkhodaei, was willing to admit that a 100%+ turnout had “happened in only 50 cities” (not the 80-170 that had been claimed). He also maintained that “the vote tally affected by such issues could be over 3 million and would not noticeably affect the outcome of the election.”

Nate Silver at fivethirtyeight.com headed this “Worst. Damage Control. Ever.”, and Mark Blumenthal at Pollster.com, while being slightly more charitable to the Iranians, noted that “it’s quite a stretch.”

Election irregularities are a matter of degree. There is no such thing as a perfectly-run election; something will always go wrong, however minor. In the case of what one might call routine irregularities, the question to ask is whether, given the margin involved, they were large enough to have possibly changed the result. (This was the question the federal court had to address after the 2007 disputed election in McEwen.)

But when it comes to the sort of large-scale fraud that can only happen with the connivance of the authorities, that is the wrong question to be asking. If officials say, in effect, “Yes, we systematically rigged the election and defrauded millions of people of their votes, but it didn’t really make a difference, because our candidate would have won anyway”, the proper response is not, “Oh, that’s OK then.”

The proper response is the one that Iran’s citizens have been expressing in the streets. More power to them.