St. Mary's College of Maryland
During political campaigns the spread between the popularity of the candidates is a common metric capturing the state of the horse-race feature of the campaign. One candidate is said to be ahead of another by an indicated number of percentage points. If the difference is less than the margin of error, the race is considered too close to call. In two-person races, however, the spread corresponds to a much smaller confidence level than is usually reported because the two numbers used to compute the spread are not independent. The size of the confidence interval that is typically reported is incorrect by a factor of two. Therefore, some spreads that are reported as decisive are races too close to call.
Walter W. Hill is professor of political science at St. Mary's College of Maryland. He can be reached at firstname.lastname@example.org.