Andrew Martin and Kevin Quinn defend their estimates of ideological positions of Supreme Court justices

A couple days ago, I wrote, of Martin and Quinn’s estimated positions of Supreme Court justices, that

I don’t know whether to believe the numbers. Is the Anthony Kennedy of 2007 (ideology score 0.14) really so close to Hugo Black in 1970 (ideology score 0.06)? To look at it another way, according to these numbers, in 1973 (the year of Roe v. Wade), six of the justices are colored red and the median justice is listed at 0.67. In 2007, only five are red and the median is at 0.14. In fact, in 2005 the median is listed as -0.07, or slightly to the left of center. Is it really plausible that the court was more liberal in 2005 than in 1973? Maybe so, but something looks fishy to me here.

In reply, Andrew Martin wrote:

re: Black and Kennedy, I [Martin] tend to think of them as pretty similar. Both were moderates (although on somewhat different types of cases), one a moderate Dem the other a moderate Rep. So them being close is not implausible.

There were a couple of very liberal decisions in the 1972 term (when Roe was decided), including a Roe and a death penalty case. But even on civil liberties the court reached a conservative decision in Miller (the obscenity case). And there were some more conservative decisions in other areas of law. Today’s court is surely more conservative on civil liberties issues (although there haven’t really been many cases…), but may be a little to the left on some other issues (Hamdan). Today it all gets down to what Kennedy wants to do. If it were what Roberts would do the court would be far to the right.

That’s an argument for plausibility, but the argument may be implausible. We tend to think about the Court in terms of the most politically salient cases, but the model treats Roe as equally to, say, a tax case. And, of course, the measures have huge limitations because they are just based on binary data, on all cases, with some reasonably strong model assumptions, etc.

The point about counting different domains of the law is interesting, along with the age-period-cohort sort of question of how you can even try to align left-right today with the corresponding positions in 1972.

2 thoughts on “Andrew Martin and Kevin Quinn defend their estimates of ideological positions of Supreme Court justices

  1. While I haven't read the study–only looked at the graphs–one of the things that tends to happen is the political ideology of the parties shifts, but not the court which is anchored in judicial theories more than shifting political ideologies.

    For example, Hugo Black was put into place by FDR in part because he rejected the idea of a substantive due process clause, the "left" position at the time. Later, when it came time for Griswold vs. Connecticut (which has drawn criticism as "judicial activism" by conservatives) and substantive due process was used to justify a right to privacy, he rejected it and dissented. Is it really accurate to say that he shifted to the right relative to his peers?

    Basically: I'm suspicious of anything that attempts to track this sort of thing on a linear scale over time when there is a moving political environment.

  2. Isn't there a problem in interpretation with using a single conservative/liberal dimension to model the court? I'd think getting good predictive power would require more dimensions. Of course, that brings up interpretation of the latent factors.

    Gelman and Hill's regression book covers ideal-point models for supreme court voting, and they suggest identifying the model by fixing the position of a judge with known liberal or conservative leanings (e.g. fixing Clarence Thomas to position 1.0) and interpreting everyone else relative to that position.

    I just had the pleasure of seeing Burt Monroe present some joint work with Kevin Quinn on analyzing positions in the congressional record to discover relations between the text of their speeches and their votes. I thought I remembered seeing two-latent factors (aka "random effects") in the model. Kevin's also done some really nice work (with Dan Ho) on newspaper editorial text and their political positions (more ideal point models).

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