George,

There is another glaring methodological error in the SurveyUSA poll beyond those that the Perriello campaign pointed out. SurveyUSA polls are usually conducted in one day – at least the one conducted in the 5th district in 2008 was. One-day polling is in complete violation of THE fundamental rule of scientific sampling: that everyone in the district (of voting age) has an equal chance of being selected. In order to achieve this, phone numbers must be dialed at different times of day for several days until the respondent is reached. Otherwise the poll misses a great many people who do not happen to be at home on the day and at the moment the call comes. All reputable polls are conducted over several days for this reason.

Also, did SurveyUSA dial cell phone numbers? A great many people, especially younger ones, no longer have land phones. All reputable pollsters are now including cell phone numbers in their samples.

David RePass (Electronic Mail, July 23, 2010)