By now hundreds of statistically minded people are poring over Iranian election data. Here's part 1 of my analysis, which is also cross-posted at the Princeton Election Consortium.
Three general categories of data are currently available for validating the Iranian election: (1) pre-election polls, (2) statistical methods for analyzing standalone voting data, and (3) statistical comparisons with past elections. In this diary I examine pre-election polls, which when aggregated under normal conditions are very good measures of sentiment.
A simple look at pre-election polls leads to the following assessment: National Iranian polls were highly variable and of suspect quality. But within Tehran, polls were more uniform and allow a comparison. Six Tehran polls gave a median lead for Moussavi by 4%. This differs notably from the official tally for the city, Ahmadinejad by 12%. The 16-point discrepancy suggests an anomaly in Tehran and opens the question of whether fraud occurred here - and elsewhere. However, it is also important to note several caveats, including polling uncertainty and possible shifts in opinion following the Ahmadinejad-Moussavi debate on June 3rd.
Details after the jump.