Recent writings concerning the measurement of political democracy offer sophisticated discussions of the problems of conceptualization, operationalization, and aggregation. Yet they have less to say about the error that derives from the use of inaccurate, partial, or misleading data sources. Drawing on evidence from five Central American countries, we show that this data-induced measurement error compromises the validity of the principal, long-term cross-national scales of democracy. In response, we call for an approach to index construction that relies on case expertise and the use of a wide range of data sources. We employ this approach in developing a new index of political democracy for the Central American countries during the 20th century. The index draws on a comprehensive set of secondary and primary sources even as it rigorously pursues standards of conceptualization, operationalization, and aggregation. We illustrate the value of the index by showing how it suggests new lines of research in the field of Central American politics.

NOTE: Our index is dynamic in the sense that new data or sources may refine our coding of individual dimensions for individual years, particularly in the early part of the 20th century. If you believe that our current dataset has errors or shortcomings, please contact the authors (kirk.bowman@inta.gatech.edu, fabrice.lehoucq@cide.edu, James_Mahoney@brown.edu).