Just Weight! The Case for Dynamic Party Identification Weighting

Abstract

W eighting survey data based on so cial background characteristics such as age, education, gender, and race is a standard practice in public opinion polling. By adjusting the composition of their samples to conform to known de mographic characteristics of the popu lation, pollsters greatly increase the accuracy of their results. However, with the exception of the Zogby Poll, most major polling organizations, including the Gallup Poll, have strongly opposed weighting their data based on party iden tification. This opposition is understand able. Party identification is not a fixed characteristic of the electorate. It is a political attitude that can vary over time. As a result, most pollsters believe that there is no way of accurately determin ing the underlying distribution of party identification in the population for weighting purposes. Although party identification is an atti tude and not a fixed characteristic, politi cal scientists have long recognized that it is a very stable attitude. Gradual shifts in the balance of party loyalties in the elec torate are not unusual-Republicans have gained ground in relation to Democrats in recent years, for example. However, dra matic changes over a short period of time are quite rare. This conclusion is sup ported by decades of research on parti sanship in the American electorate and has been confirmed recently by the work of Green, Palmquist, and Schickler. In Partisan Hearts and Minds (2002), they demonstrate that party identification is largely immune to changes in economic conditions, presidential popularity, and other short-term events. While the resistance of most polling organizations to the use of party identifi cation weighting is understandable, evi dence from recent Gallup Polls indicates that allowing the proportions of Demo crats, Republicans, and independents to vary from sample to sample without any constraint produces unrealistically large swings in estimates of party identifica tion and other attitudes that are strongly influenced by party identification, such as presidential approval. I propose a so lution to this problem that does not re quire a rigid assumption about the underlying partisan composition of the electorate: dynamic party identification weighting using moving average esti mates of the partisan composition of the electorate based on multiple polls done over several weeks. Between January 1 and August 7, 2005, the Gallup Poll conducted 24 sepa rate national surveys in which respon dents were questioned about their party identification. Figure 1 displays the trend in the Democratic-Republican party iden tification differential-the percentage of Democratic identifiers and leaners minus the percentage of Republican identifiers and leaners-in these 24 surveys. The most striking feature of this se ries is its volatility. Across all 24 polls, there was an average Democratic advan tage of 3 percentage points. This was identical to the average for all Gallup