Gay marriage and the null hypothesis

Two controversial topics in one post!

Orin Kerr this week on Perry vs. Schwarzenegger:

Several of the key factual findings in Judge Walker’s opinion are in the form of predictions, not facts. For example, Judge Walker finds that “permitting same-sex couples to marry will not . . . otherwise affect the stability of opposite-sex marriages.” But real predictions have confidence levels. You might think you’re going to get an “A” on an exam next week, but that’s not a fact. It’s just a prediction, and there’s a hidden confidence level: Maybe there’s an 80% chance you’ll get that grade, or a 60% chance. Judge Walker’s prediction-facts have no confidence levels, however. He doesn’t say that there is an 87% chance that permitting same-sex marriage will not affect the stability of opposite-sex marriages. He says that it is now a fact — with 100% certainty — that that will happen.

I think Kerr is incorrect about Walker’s meaning.  When we say, for instance, that a clinical trial shows that a treatment “has no effect” on a disease, we are certainly not saying that, with 100% certainty, the treatment will not change a patient’s condition in any way.  How could we be?  We’re saying, instead, that the evidence before us gives us no compelling reason to rule out “the null hypothesis” that the drug has no effect.  Elliott Sober writes well about this in Evidence and Evolution.  It’s unsettling at first — the meat and potatoes of statistical analysis is deciding whether or not to rule out the null hypothesis, which as a literal assertion is certainly false!  It’s not the case that not a single opposite-sex marriage, potential or actual, will be affected by the legality of same-sex marriage; Walker is making the more modest claim that the evidence we have doesn’t provide us any ability to meaningfully predict the size of that effect, or whether it will on the whole be positive or negative.

This doesn’t speak to Kerr’s larger point, which is that Walker’s finding of fact might not be relevant to the case — California can outlaw whatever it wants without any evidence that the outlawed thing causes any harm, as long as it has a “rational basis” for doing so.  The key ruling here seems to be Justice Kennedy’s in Heller v. Doe, which says:

A State, moreover, has no obligation to produce evidence to sustain the rationality of a statutory classification. “[A] legislative choice is not subject to courtroom factfinding and may be based on rational speculation unsupported by evidence or empirical data.”

and later:

True, even the standard of rationality as we so often have defined it must find some footing in the realities of the subject addressed by the legislation.

I’m in the dark about what Kennedy can mean here.  If speculation is unsupported by evidence, in what sense is it rational?  And what “footing in the realities of the subject” can it be said to have?

More confusing still:   in the present case, the legislation at issue comes from a referendum, not the legislature.  So we have no record to tell us what kind of speculation, rational or not, lies behind it — or, for that matter, whether the law is intended to serve a legitimate government interest at all.  Maybe there is no choice under the circumstances but for the “rational basis” test to be no test at all, and for the courts to defer completely to referenda, however irrational they may seem to the judge?

(Good, long discussion of related points, esp. “to what extend should judges try to read voters’ minds,” at Crooked Timber.)

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6 thoughts on “Gay marriage and the null hypothesis

  1. harrison says:

    “So we have no record to tell us what kind of speculation, rational or not, lies behind it — or, for that matter, whether the law is intended to serve a legitimate government interest at all.”

    The way the rational basis test is applied, the original intent of the law actually doesn’t matter. As long as the government can argue that there is some legitimate reason to have a law that “deprives [a citizen] of life, liberty, or property”, due process isn’t considered to have been violated.

    But in cases involving discrimination involving “quasi-suspect classes,” which gay people are considered to be, it’s not uncommon for a court to claim it’s applying rational basis review but actually apply a sort of balancing test, judging whether the claimed interest to which the law is supposedly related outweighs the interest in treating that class equally. So, no, California wouldn’t have to prove that gay marriage hurts opposite-sex marriage — but it would have to prove that “protecting traditional marriage” is a strong enough interest to justify discrimination.

  2. I read through a good part of Walker’s opinion, and I think perhaps a more accurate summary on this point is “the defense (pro-prop 8) presented no evidence whatsoever that same-sex marriage will otherwise affect the stability of opposite-sex marriages, and so therefore I conclude there isn’t any”. The defense presented essentially only one witness for most of the issues disputed, and in the end Walker ruled that he was not sufficiently expert for his opinion to be seriously considered, and regardless his testimony was pretty incoherent much of the time.

  3. Also, on the final issue of how to determine what kind of speculation the voters made when approving it, there was actually some testimony a trial devoted to this. The plaintiffs called the head of the pro-8 campaign as an adverse witness, and also had experts testify about the background of previous such referenda (e.g. the one that Harvey Milk helped defeat in the 70s) and what groups supported Prop 8, etc.

  4. I have no idea if this is what was meant, but one type of “rational speculation unsupported by evidence or empirical data” which still has “some footing in the realities of the subject” which occurs to me immediately is applying established theories to new domains. So you could have a law which bans putting cyanide in energy drinks, without having to establish that, yes, it really still kills you even when it’s in solution with caffeine. Or, relying on the general economic principle that monopolies lower welfare by producing too little and charging too much, you could extend anti-trust law into new industries, without waiting for econometric studies establishing that, yes, that happens with widget-making (or foobar-service-provision) too.

  5. harrison says:

    Definitely it didn’t hurt the gay marriage case that the Prop 8 defenders were borderline incompetent. But I’m not sure that’ll remain true throughout the appeals process.

  6. Gay marriages suck, with or without hypothesis.

    What if the couple decides to adopt a child. What will happen to the kids sexual orientation?

    If hetero-people are “forcing their point of view” on homo-children, then what a about a homo-couple with a hetero-child ???!!!

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