Tom Pepinsky

Category: Research

  • Learning from Marginal Effects Plots

    I really enjoy thinking about how to present quantitative information in a visual format rather than in boring tables of digits. However, at the same time, I think that many common ways to visualize quantitative results in political science are actually misleading. How can I hold both of these views at the same time?

    The answer is, because we use heuristics to interpret what the information presented in a figure means, and I think that these heuristics are often faulty. And this is more likely when we adopt a disciplinary conventions for presenting results in certain ways, such that these heuristics become so widely shared and automatic that we do not consciously think about them. In this way, I disagree somewhat with the conclusions in Kastellec and Leoni (ungated PDF) who argue that graphs enhance communication relative to tables. I think that graphical presentation of data can do this when we know that both the sender and the receiver speak the same language competently. I made this point some years ago in a presentation to Cornell graduate students (PDF).

    The example that brings this to mind is the marginal effects plot, popularized by Brambor, Clark, and Golder (2006) (PDF). These are used to visualize how the effect of one variable varies according to the value of another variable. Like this.

    MFX

    I’ve written up a little essay that illustrates how one common visual heuristic for interpreting these marginal effects plots can result in misleading inferences. Does this figure tell us that the effect of D depends on X? The answer may surprise you.

    The problem here is not with the plot itself—the plot does not create information that would not be available if the same data used to draw the lines and bars were presented in a tabular format. The problem is also not the calculation of those lines and bars. The problem is the heuristic through which these are interpreted. One might say, “yes, don’t use that heuristic,” and I agree.

    As a postscript, here is a slideshow that includes some of my favorite figures from my own published and unpublished work. I’m sure by some other objective standard (perhaps Tufte‘s) these are ugly, but I think they are effective and that is what I care about. And because you don’t have a ready-made heuristic about how to interpret them, it’s more likely that you’ll slow down and look at them.

     

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  • The Long Arm of Western Crises

    What seems a lifetime ago, I wrote a short essay for the newsletter of the International History and Politics section of the American Political Science Association. Here is how it begins:

    The events of 2016 represent no less than a crisis of democracy and capitalism in the West. Not since the 1970s have the fundamental pillars of the post-war global economic order been so contested, and the future course of democracy so uncertain. A particular version of nativist populism that combines economic grievances with deep suspicion of regional institutions is now ascendant from the U.S. to Poland and Hungary. The parallels with the 1930s—also a time of economic hardship, challenges to democracy, and skepticism of international institutions—are all too evident.

    At present, the focus of debate is mostly local: what are the consequences of Donald Trump’s presidency for U.S. politics; of Brexit for the U.K. economy; of Geert Wilders, Marine Le Pen, Heinz-Christian Strache, Frauke Petry, and Viktor Orbán for the European project? What remains is geostrategic: what is the future of NATO; of U.S.-China relations; and of Russia as a Eurasian power? From the perspective of global history and politics, what interests me are the as-yet unanticipated consequences of this crisis beyond the borders of Europe, North America, and their great power rivals. The West’s political and economic crises tend to have long arms; witness, for example, the Latin American debt crises that followed from economic slowdowns in the U.S. and Europe in the early 1980s. In the context of the current crisis, what does the future hold beyond the borders of the North Atlantic community, in particular for the global South?

    You can read the full thing, alongside thoughtful and interesting essays by Deborah Boucoyannis, Margaret Peters, and Stefanie Walter, here (PDF).