Published online by Cambridge University Press: 04 January 2017
The Comparative Manifesto Project (CMP) provides the only time series of estimated party policy positions in political science and has been extensively used in a wide variety of applications. Recent work (e.g., Benoit, Laver, and Mikhaylov 2009; Klingemann et al. 2006) focuses on nonsystematic sources of error in these estimates that arise from the text generation process. Our concern here, by contrast, is with error that arises during the text coding process since nearly all manifestos are coded only once by a single coder. First, we discuss reliability and misclassification in the context of hand-coded content analysis methods. Second, we report results of a coding experiment that used trained human coders to code sample manifestos provided by the CMP, allowing us to estimate the reliability of both coders and coding categories. Third, we compare our test codings to the published CMP “gold standard” codings of the test documents to assess accuracy and produce empirical estimates of a misclassification matrix for each coding category. Finally, we demonstrate the effect of coding misclassification on the CMP's most widely used index, its left-right scale. Our findings indicate that misclassification is a serious and systemic problem with the current CMP data set and coding process, suggesting the CMP scheme should be significantly simplified to address reliability issues.
Authors' note: Previously presented at the 66th MPSA Annual National Conference, Palmer House Hilton Hotel and Towers, April 3–6, 2008. Our heartfelt thanks goes out to all the volunteer test coders who completed the online coder tests used in the research for this paper. We also thank Andrea Volkens for cooperation and assistance with details of the coding process, and Jouni Kuha, Michael McDonald, Michael Peress, Sven-Oliver Proksch, Jonathan Slapin for useful comments. For replication data and code, see. Supplementary materials for this article are available on the Political Analysis Web site.