Abstract
Voting Advice Applications (VAAs), such as the German Wahl-O-Mat (WOM), have been examined extensively by researchers in various ways. Here, a subset of research uses data from the Wahl-O-Mat to investigate party relations. While these investigations focus on a limited number of WOM editions, I explicitly investigate the persistence of party relations in the WOM in a broad statistical analysis over 63 editions of the WOM in this exploratory research paper. At first glance, I find that intuitive differences in the overall proximities are observable. However, while many arguments exist that corroborate the suitability of the WOM data for the investigation of party relations, I identify statistically significant lower proximities for the six largest German parties in WOM editions from 2009 onward. Based on a review of changes in the design framework of the WOM and comparative data analyses based on the Chapel Hill Expert Survey and the Manifesto data set, these lower proximities are apparently linked to changes in the design of the WOM. As a result, I discuss the general ability of data from the WOM to give reliable insights into party relations. I argue that the WOM might roughly represent overall party relations but, due to a non-proportionality in the shift of the distances, potential design changes have distorting impacts on the relations between parties that make comparisons between different editions of the WOM problematic. This should be a starting point to investigate other VAAs for similar patterns to reevaluate the validity of data from VAAs for the examination of party relations in general.
Acknowledgment
I want to thank Prof. Dr Dominik Wied for all his helpful advice for my research. Next, I want to thank Felix Boelte for his hints on existing literature as well as his comprehensive provision of WOM data. Further, I want to thank Prof. Dr Alexia Katsanidou, Prof. Dr Diego Garzia, as well as two anonymous peer reviewers for their constructive and helpful feedback.
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Research funding: I did not receive any funding for this work.
A.1 Equality of Dummy-Variable Approach and Normed Manhattan Distance
If a measure of similarity fulfills 0 ≤ s(x i , x j ) ≤ 1, it can easily be transformed into a measure of distance by 1 − s(x i , x j ) = d(x i , x j ) (Backhaus et al. 2016, p. 498). Since the matching coefficient obviously fulfills this condition, it can simply be converted into a measure of distance:
Here,
Since the K − 1 dummy variables code the deviation of the reached expression level from the baseline in the variable p,
A.2 Empirical Comparison of Proximity Measures
While discussing the proximity measures theoretically, I further test their performance on the WOM data in practice. As mentioned above, the Manhattan and Euclidean distances are normalized to enable a sensible comparison between the WOMs as well as between the proximity measures. To further enable a comparison, the matching coefficient is reformulated as a measure of distance via 1 − sMat(x i , x j ) which I refer to as the non-matching coefficient. Since measurements based on the Manhattan distance are preferred from a theoretical perspective, it is considered to be the “gold standard”. Figure 4 illustrates the pairwise scatterplots for the three different measures.

Plots of the pairwise distance measurements for the 788 pairwise distance measurements of the six parties. The colored lines represent the bisectrix.
I find the correlation of the normed Euclidean and the normed Manhattan approach with 0.99 to be the highest, the Manhattan and the non-matching coefficient to be correlated with 0.975, and I find a correlation of 0.949 for the normed Euclidean distance and the non-matching coefficient. While these correlations seem to be high at first glance, the inspection of the scatterplots reveals deviations in the measurements: For example, for a normed Manhattan distance of 0.5, the measurements of the normed Euclidean distance lie between approximately 0.62 and 0.70 while the measurements of the non-matching coefficient lie between 0.56 and 0.68. However, for a normed Euclidean distance of 0.5, we observe an even larger range for the measurements of the non-matching coefficient of approximately 0.22.
Further, it is possible to identify the discussed tendencies of the proximity measures. First, the (normed) Euclidean distance generally shows larger measurements than the (normed) Manhattan distance. This seems to be especially the case for measurements of the normed Manhattan distance below 0.4. While the distance measurements of the non-matching coefficient also show higher maximum distances, the deviations from the measurements based on the Manhattan distance are highly dispersed. This seems to be especially the case for an increasing normed Manhattan distance. For the sake of completeness, I also compare the normed Euclidean distance to the non-matching coefficient which reveals an even higher dispersion. It is salient that the measurements of the Euclidean distance tend to be higher for lower measurements of the non-matching coefficient, while the measurements tend to scatter around the bisectrix for higher measured distances.
This practical examination demonstrates the potential overweighting of larger deviations of the Euclidean distance and the overestimation of general distances by the (non-)matching coefficient. Hence, these results underline the theoretical considerations.
A.3 MWU Test-Statistic
For sizes of the pooled sample n > 50 and ties in the ranks, the test statistic and the respective (approximative) distribution under H0 are given by
with R1, R2 denoting the rank sums of subsample 1 and 2 respectively.
A.4 Figures

Boxplots of the distances for all party combinations.

Depiction of the normed Manhattan distances for SPD/FDP (yellow) and SPD/Greens (green) over all 63 WOMs indicated by the date of the respective election.
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Articles in the same Issue
- Frontmatter
- Articles
- Party Proximities in Voting Advice Applications – Identifying Structural Breaks in Data from the German Wahl-O-Mat
- A Geometric Model of Elections in Five Federal Democracies
- Hybrid Modeling Techniques for Municipal Solid Waste Forecasting: An Application to OECD Countries
- The Great Powers Competition and Increasing Entropy in the Local Media Across Africa and Asia
- Hierarchical Bayesian Modelling of Macroeconomic Variables in Ghana
Articles in the same Issue
- Frontmatter
- Articles
- Party Proximities in Voting Advice Applications – Identifying Structural Breaks in Data from the German Wahl-O-Mat
- A Geometric Model of Elections in Five Federal Democracies
- Hybrid Modeling Techniques for Municipal Solid Waste Forecasting: An Application to OECD Countries
- The Great Powers Competition and Increasing Entropy in the Local Media Across Africa and Asia
- Hierarchical Bayesian Modelling of Macroeconomic Variables in Ghana