by Michael Lowrey
From someone that really should know better, talking about the presidential race in North Carolina:
“We’ve seen so much volatility in this race, so you can move from a deadlocked race to a 5 percentage point race over a matter of days,” said David McLennan, a political science professor at William Peace University in Raleigh./blockquote>
Wrong. A poll is but a small sample of the (voting) population. As Wikipedia explains:
A 3% margin of error means that if the same procedure is used a large number of times, 95% of the time the true population average will be within the 95% confidence interval of the sample estimate plus or minus 3%. The margin of error can be reduced by using a larger sample, however if a pollster wishes to reduce the margin of error to 1% they would need a sample of around 10,000 people. In practice, pollsters need to balance the cost of a large sample against the reduction in sampling error and a sample size of around 500–1,000 is a typical compromise for political polls. (Note that to get complete responses it may be necessary to include thousands of additional participators.)
The WRAL poll which prompted McLennan’s comments had a 3.8 percent margin of error. The underlying voter preferences may or may not be changing over time — different samples (polls) of the same population can and will give different figures even if no one has changed their mind. So “so much volatility” may not be volatility at all.