Op-scan machines tended to be used in counties with small numbers of registered voters, while very largest counties tended to used E-touch, so that the entire two groups of counties (E-touch and Op-scan users in Florida) cannot be validly compared, as county-size itself might account for the data. However, for the 26 mid-sized counties with between 80,000 and 500,000 registered voters, the type of machine used was not significantly related to the number of registered voters in the county. Eight of these counties used E-touch machines, and 18 used Op-scan machines. There was no significant difference between these two groups of counties in either their numbers of registered voters or their proportion of registered Republicans to registered Democrats. Neither covariate was a significant predictor of change. However, "machine used" was very significant (p<.01), with Op scan favoring repubs.
An analysis of variance (ANOVA) conducted on the percent change for each party ([Actual vote minus expected vote]/expected vote) in each county, with "machine type" as a predictive factor, indicated that machine type was a significant predictor of percent change in voting. Counties using E-touch machines showed significantly positive percent changes in vote for both Republican and Democrat candidates, with greater mean percent changes for the Democrat. However counties using Op-scan machines showed significant positive percent change only for the Republican candidate, the mean change for the Democrat being insignificantly greater than zero.
Caveats: The number of counties is small, and the groups unequal in size; this means that the probability of the results occurring by chance may be somewhat greater than quoted. It is also possible that a county's choice of machine or voting pattern may be influenced by a third factor that also influenced voter behaviour. The magnitude of the apparent effect of voting machine type on voter behaviour nonetheless would seem to warrant investigation.
Elizabeth Liddle