A two-dimensional analysis of seventy years of United Nations voting


International relations scholars frequently use roll-call votes on resolutions in the United Nations General Assembly (UNGA) to measure similarity in the foreign policy ideologies of states. They then correlate those measures with consequential outcomes, such as development lending, trade, or military disputes. Dynamic ideal point models of UNGA voting thus far have been restricted to a single dimension. We examine the existence of a stable, important, and interpretable second dimension underlying contestation in the UN. From the mid-1960s to the mid-1980s, North–South conflict constitutes a stable second dimension, shaped heavily by the agenda-setting powers of the so-called Non-aligned Movement and the Group of 77. In the periods before and after, the second dimension neither is stable nor easily interpretable, though it is sometimes important. We suggest that in most applications, our original one-dimensional estimates have conceptual advantages with minimal losses in explanatory value. We illustrate that conclusion with an analysis that correlates ideal point changes with militarized interstate disputes. Yet, our findings also suggest that scholars interested in specific issues, such as the Middle East, human rights, or arms control, might benefit from more specifically tailored ideal point estimates.

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  1. 1.

    Voeten also used this approach to analyze the immediate post-Cold War period (Voeten 2004).

  2. 2.

    Estimating the model on leaders (or governments) rather than states does not solve the problem. For example, the Soviet Union changed its position during Mikhail Gorbachev’s tenure. Brazil swiftly altered its foreign policy position (and its UNGA voting behavior) under military dictatorship in the mid-1970s following a strategic decision to seek allies in the developing world.

  3. 3.

    Another challenge addressed by BSV was that UN data is ordinal because abstention is used to express a middle position between yea and nay on many resolutions. That situation contrasts with many legislative voting contexts where abstention tends to reflect actual absence, leading scholars to use only dichotomous voting data in their analyses.

  4. 4.

    Of the 4975 roll calls analyzed across all sessions, 3707 had yea, abstain and nay votes, 1068 roll calls had only yea and abstain votes, 198 roll calls had only yea and nay votes and two roll calls had only abstain and nay votes. Votes with only two observed voting choices were treated as dichotomous, obviating the need to estimate \(\gamma _{v}\) for them.

  5. 5.

    Specifically, we use the ordfactanal procedure in MCMCPack. That procedure simulates from the posterior distribution of the parameters using a hybrid Gibbs and Metropolis–Hastings sampling algorithm. For the \(\lambda\) and \(\theta\) parameters, a Gibbs sampler produces draws from the marginal distribution of each parameter. The marginal distribution of the \(\gamma\) parameter is not easily amenable to a Gibbs sampler, so a Metropolis–Hastings rejection-based sampling process is used. More details are available in Martin et al. (2011) and in the appendix of Bailey et al. (2017).

  6. 6.

    Other two-dimensional models define the polarity of one resolution on each dimension and sett the discrimination parameter for one resolution on the second dimension to zero. In our model, the strong informative priors on the first dimension mean that we need to define polarity only on the second dimension. We chose resolutions with high variances (i.e., considerable proportions of countries on the minority side).

  7. 7.

    That is an interesting issue in Poole and Rosenthal, as the meaning of the second dimension has evolved over time. By estimating a single model, the second dimension in the 1990s is forced to have some consistency with the very strong civil-rights-related second dimension of the 1960s, even if the second dimension has evolved to relate to a different set of issues on which legislators had different preferences.

  8. 8.

    The equations for the cutting lines are: \(y=-\frac{\lambda _{0}}{\lambda _{2}}-\frac{\lambda _{1}}{\lambda _{2}}x\) and \(y=-\gamma -\frac{\lambda _{0}}{\lambda _{2}}-\frac{\lambda _{1}}{\lambda _{2}}x.\)

  9. 9.

    No UNGA votes were taken in 1964.

  10. 10.

    Roughly one-quarter of the votes were dichotomous because, as discussed earlier, only two vote choices were observed for them. In general, yea votes predominate (constituting 79% of all votes), a pattern that makes model fit easier relative to a situation in which voting is split more evenly across the yea, abstain and nay options.

  11. 11.

    The higher MSE and lower GMP in the 1950s may also have been explained in part by to the fact that the UNGA had fewer voting members then.

  12. 12.

    The credible intervals are computed from the standard deviations of the mean in the posterior distributions.

  13. 13.

    The horseshoe in this case has a substantive interpretation and is not an artifact of multidimensional scaling (Diaconis et al. 2008).


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Correspondence to Erik Voeten.

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Bailey, M.A., Voeten, E. A two-dimensional analysis of seventy years of United Nations voting. Public Choice 176, 33–55 (2018). https://doi.org/10.1007/s11127-018-0550-4

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  • United Nations
  • International relations
  • International organizations
  • Ideal point estimation