|Perl Monk, Perl Meditation|
Assessing a statistical argument on the fraudulance of the Iranian electionsby whakka (Hermit)
|on Jun 23, 2009 at 02:32 UTC||Need Help??|
Update: Fixed to address the actual test used, which I originally misread, from which what they calculate is numerically accurate.
A lot of attention has been garnered by the Washington Post article with a statistical argument that the elections in Iran were a fraud. I replicate part of it below with my critique of what it all means.
Their argument goes like this: A random draw from the digits 0-9 yield a 10% probability of picking any single digit. In the election results the digit 5 occurred as the last digit 4% of the time while the digit 7 similarly occurred 17% of the time. (Apparently this also had some psychological significance.)
"Fewer than four in a hundred non-fraudulent elections would produce such numbers."
A testable assertion! Onto the Perl: (note that the election results had 116 observations)
So, from a uniform distribution between 0-9 of 116 random draws you would expect to find one digit occurring 4% of the time or fewer in over 20% of the cases. The odds of a digit occurring 17% of the time or higher is half as frequent yet still comfortably inside the 95% confidence interval. We fail to reject the null hypothesis of both individual tests at the 5% level,
The fact remains they used arbitrary tests to arrive at this number - you would have to believe each psychological justification to say it bears any significance. It also reeks of data mining - they omit to tell us if they tested other bits of psychological trivia that happened to turn out non-significant. If they did then their final likelihood assessment - 1 in 200 - is invalid, and they should have instead pooled all of their tests, significant or not.
Election fraud is a serious charge and one that should be made with stronger evidence than a few minor statistical anomalies based on flimsy ad-hoc reasoning. Analyses based on exit polling data, for example, are much more sound - if systematic anomalies are observed you either have to reject the polling methodology (sample bias, eg) or question the election results.