The data are observations on the difference between Democratic and Republican vote counts, by (a) absentee ballot and (b) voting machine, for 22 elections in Philadelphia's senatorial districts over the last 10 years.
A data frame with 22 observations on the following 2 variables.
Democratic minus Republican vote count by absentee ballot
Democratic minus Republican vote count by voting machine
Ramsey, F.L. and Schafer, D.W. (2002). The Statistical Sleuth: A Course in Methods of Data Analysis (2nd ed), Duxbury.