Cognitive psychologists have found that people have trouble inventing truly random numbers. Invariably their numbers will have more of some digits than others. Armed with this observation, a couple of political scientists examined the numbers from Iran's election and found that they aren't random. They found too many 7s and not enough 5s in the last digit.
Also, people have a tendency to prefer adjacent digits when creating strings of numbers (i.e. they prefer 123 to 926). Sure enough, the election figures from Iran contain a suspiciously high percentage of adjacent digits. Washington Post