In the first section, the concept of electoral integrity is treated as a component of liberal democracy, as this conceptualization largely determines how integrity is empirically specified and measured, although differing from the human rights approach discussed in the book’s introductory chapter. The second section describes the specification of PEI survey components and reviews previous research on the challenges of configuration, aggregation, and measurement of such indices. Empirical tests assess equivalence between the global and U.S. PEI data sets. Both statistical and case analysis help to determine whether expert respondents are measuring the same thing, in the same way, given use of the same indicators. The third section compares the PEI index with alternative U.S. electoral integrity measures, assessing the degree to which indicators are measuring the same components of electoral integrity. Deviations between these indices are analyzed and potential sources of bias are explored. The final section reconsiders the potential of a general measure of electoral integrity in light of the analysis and provides suggestions for avoiding bias in future electoral integrity research.