4.10 Not in the margin of error. According to a February 2008 USA Today/Gallup Poll, 43% of Americans identify themselves as baseball fans. That is low by recent standards, as an average of 49% of Americans have said they were fans of the sport since Gallup started tracking this measure in 1993. The high point came in 1998, when Sammy Sosa and Mark McGwire pursued (and ultimately surpassed) Roger Maris’s single-season home run record, at which time 56% of Americans considered themselves baseball fans. The Gallup press release says:

For results based on this sample, one can say with 95% confidence that the maximum error attributable to sampling and other random effects is ±5 percentage points.

Give one example of a source of error in the poll result that is not included in this margin of error.