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Reply to Benoit and Laver

Published online by Cambridge University Press:  06 August 2007

Lanny W. Martin
Affiliation:
Department of Political Science, Rice University, PO Box 1892, MS 24, Houston, TX 77251-1892, e-mail: lmartin@rice.edu
Georg Vanberg
Affiliation:
Department of Political Science, University of North Carolina, Chapel Hill, Chapel Hill, NC 27599-3265, e-mail: gvanberg@unc.edu
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We appreciate the positive reception of our transformation by Benoit and Laver (hereafter, BL), and we are grateful that they have incorporated it into the Wordscores package. Because their comment highlights a fundamental difference between the Martin-Vanberg (MV) and Laver-Benoit-Garry (LBG) approaches that is critical to the choice among transformations, we offer some brief comments that will allow users to make an informed decision regarding the appropriate use of the transformations. The central issue concerns comparisons between reference and virgin texts. As BL point out, researchers will often be interested in making such comparisons, and the LBG and MV transformations can yield substantially different results. In light of these differences, BL's primary suggestion is to focus analysis on the raw scores, which can be obtained for reference as well as virgin texts. We wholeheartedly agree with this prescription. In fact, it is precisely a concern for faithfully reporting the raw score information, while making it more intuitive, that motivates the MV transformation. As we show below, the MV transformation accurately reflects all and nothing but the information contained in raw scores. Therefore, “users [who] get eye strain” by looking at raw scores can safely substitute MV scores and be confident that the information provided is equivalent. The same will typically not be true of LBG scores.

Type
Letter
Copyright
Copyright © The Author 2007. Published by Oxford University Press on behalf of the Society for Political Methodology 

References

1 Without further explanation, BL suggest that to judge the LD's 1997 position in relation to its 1992 position, the 1997 raw score should be compared to the mean of all reference scores rather than to the 1992 LD raw score. Such a comparison may allow an analyst to place a text relative to the center of the text distribution, but it is not relevant when trying to assess the relationship between two particular texts. To do this, the appropriate comparison is between the raw scores of the two texts in question. Finally, although it is interesting that expert surveys indicate an LD move to the left, this does not change the fact that the raw scores—which BL purport to prefer—point in the other direction.Google Scholar