What to Do (and Not to Do) with the Comparative Manifestos Project Data

The Comparative Manifestos Project (CMP) data are the most popular source for parties' positions on the leftright and other ideological and policy dimensions. Over the past few years, several researchers have identified various methodological problems in the CMP data, but third-party users rarely acknowledge them. This article classifies the problems associated with the CMP into four areas: (1) theoretical underpinnings of the coding scheme; (2) document selection; (3) coding reliability; and (4) scaling. The article reviews each area systematically and concludes with a set of recommendations regarding the use of the CMP data.