06/22/2009 07:47 pm ET | Updated May 25, 2011

Mebane Update: Ballot Box Data Shows "Significant Distortions"

Walter Mebane has once again updated his analysis of the official vote count in Iran (via Gelman), having now obtained ballot box data in 23 of 30 provinces. His modified conclusion (raw data here):

The initially released polling station data show evidence of significant distortions in the vote counts not only for Karroubi and Rezaei but also for Ahmadinejad. No significant distortions are apparent for Mousavi's vote counts. A key to interpreting these results is understanding why the vote counts for Karroubi and Rezaei are typically so small. Is it (a) inherently low levels of support, (b) voters strategically abandoning the candidates, or (c) fraudulent counts? If there is good reason to believe either (a) or (b), then (c) is less likely. The significant result for Ahmadinejad is not direct proof that Ahmadinejad's votes are fraudulent, but fraud is certainly a reasonable inference in light of reports that "Iran's Guardian Council has admitted that the number of votes collected in 50 cities surpass the number of those eligible to cast ballot in those areas" (Press TV, 2009).

Andrew Gelman, who is "inclined to believe" Mebane because he is "the expert on this stuff" (I had a similar message on Thursday) also repeats this important caveat, which is consistent with Mebane's own conclusions:

[T]his sort of statistical analysis doesn't prove anything by itself, but it can be useful in giving people a sense of where to focus attention if they want to look further.