Andrew Gelman blogged about the research of John Gottman, an emeritus professor at the University of Washington, who claimed to be able to predict whether newlyweds would divorce within 5 years with greater than 90% accuracy. These predictions were based on brief interviews near the time of marriage. Andrew agreed with another critic who said these claims were overstated. He modified Gottman’s Wikipedia page to reflect those criticisms. Andrew’s modifications were removed by someone who works for the Gottman Institute.
Were the criticisms right or wrong? The person who removed reference to them in Wikipedia referred to a FAQ page on the Gottman Institute site. Supposedly they’d been answered there. The criticism is that the “predictions” weren’t predictions: they were descriptions of how closely a model fitted after the data were collected could fit the data. If the model were complicated enough (had enough adjustable parameters), it could fit the data perfectly, but that would be no support for the model — and not “100% accurate prediction” as most people understand it.
The FAQ page says this:
Six of the seven studies have been predictive—each began with a hypothesis about factors leading to divorce. [I think the meaning is this: The first study figured out how to predict. The later six tested that method.] Based on these factors, Dr. Gottman predicted who would divorce, then followed the couples for a pre-determined length of time. Finally, he drew conclusions about the accuracy of his predictions. . . . This is true prediction.
This is changing the subject. The question is not whether Gottman’s research is any help at all, which is the question answered here; the question is whether he can predict at extremely high levels (> 90% accuracy), as claimed. Do the later six studies provide reasonable estimates of prediction accuracy? Presumably the latest ones are better than the earlier ones. The latest one (2002) was obviously not about accurate prediction estimates (its title used the term “exploratory”) so I looked at the next newest, published in 2000. Here’s what its abstract says:
A longitudinal study with 95 newlywed couples examined the power of the Oral History Interview to predict stable marital relationships and divorce. A principal components analysis of the interview with the couples (Time 1) identified a latent variable, perceived marital bond, that was significant in predicting which couples would remain married or divorce within the first 5 years of their marriage. A discriminant function analysis of the newlywed oral history data predicted, with 87.4% accuracy, those couples whose marriages remained intact or broke up at the Time 2 data collection point.
The critics were right. To say a discriminant function “predicted” something is to mislead those who don’t know what a discriminant function is. They don’t predict, they fit a model to data, after the fact. To call this “true prediction” is false.
To me, the “87.4%” suggests something seriously off. It is too precise; I would have written “about 90%”. It is as if you asked someone their age and they said they were “24.37 years old.”
Speaking of overstating your results, reporting bias in medical research. Thanks to Anne Weiss.