Pol Meth Conf IV 

 Dan Hopkins, G4, Government (guest author) 

 Continuing with the discussion of papers presented at the recent Political Methodology Conference, Kevin Quinn and Arthur Spirling's paper begins with the problem of identifying legislators' preferences in conditions of strict party discipline.  To tackle this challenge, they applied a Dirichlet process mixture model and presented some interesting results about the intra-party groups observed in the British House of Commons.  They backed up the groupings recovered from the model with significant qualitative work, and showed how qualitative and quantitative work of this kind can go hand in hand.  At the same time, the discussant, Andrew Martin, raised a valuable question: how does this method relate to other analyses of grouping/clustering?  I am curious about this question as well. 

 James Honaker's paper tackled a question of substantive importance:  what is the role of economic conditions in triggering sectarian violence?  Honaker analyzed all available data, far more than anyone previously, and used a creative combination of ecological inference and multiple imputation to estimate the impact of the Protestant-Catholic unemployment ratio on a monthly basis.  His substantive result was that this ratio matters: as the gap between Protestant and Catholic employment grows, so too does the risk of violence.  One questioner suggested that we might want to instrument for unemployment, since unemployment could be endogenous to violence.  Honaker responded that unemployment in Northern Ireland tracks unemployment in comparable cities elsewhere.  This paper struck me as, among other things, a powerful (if implicit) rebuttal to those who are that one should never attempt ecological inferences.  The question Honaker addressed is one scholars have already tried to answer - sometimes with counter-intuitive results - suggesting that we may not be able to simply wait for perfect, individual-level data. 

 Kosuke Imai presented co-authored work on an Internet experiment in Japan.  As with the Jackman et al. paper, this work presented a single Bayesian model that dealt with 1) the problem of non-compliance; 2) the problem of non-response; and 3) estimated causal effects.  The methods were compelling, although the data were less cooperative:  almost no statistically significant treatment effects emerged.  That result seems to fit with our priors: the experiment directed Japanese Internet users, presumably a relatively well-informed group, to click on a webpage containing party manifestos during the Upper House election.  The fact that we are selecting our sample based on a set of covariates might help explain why the covariates are (at least individually) relatively helpless in predicting compliance.  As with the Bowers and Hansen, I hope that the authors make their statistical code public and easily adapted to other applications-as these tools are well-suited to analyzing a wide range of randomized experiments. 

 David Epstein presented a joint paper with Sharyn O'Halloran that argued for using higher-dimension Markov models-that is, Markov models with more than two states-to model transitions to and from autocracy/democracy.  The substantive argument: adding a third category of "partial democracy" helps us see that economic growth matters both for transitioning to democracy and for staying there.  Discussant Jeff Gill and others questioned the appropriateness of the basic Markovian assumption (that the probability of transition conditional on the current state is equal to the probability of transition conditional on all previous states) and suggested exploring a higher-order Markov model (that is, models that allow previous states to influence present transition probabilities).  I agree with their suggestion, but my question is more basic: if we have polity scores that are continuous on an interval, how much information is thrown away by transforming these scores into three discrete states?  I have not seen the data, so I also wonder if these three states emerge naturally from it.  In other words, how much would this analysis change if we redefined autocracy or democracy by a few polity points?