Trump supporters are ignoring the base (rate) — Or, Ich möcht’ so gerne wissen, ob Trumps erpressen

One of the key insights from research on decision-making — from Tversky and Kahneman, Gigerenzer, and others — is the “base rate fallacy”: in judging new evidence people tend to ignore the underlying (prior) likelihood of various outcomes. A famous example, beloved of probability texts and lectures, is the reasonably accurate — 99% chance of a correct result — test for a rare disease (1 in 10,000 in the population). A randomly selected person with a positive test has a 99% chance of not having the disease, since correct positive tests on the 1 in 10,000 infected individuals are far less common than false positive tests on the other 9,999.

This seems to fit into a more general pattern of prioritising new and/or private information over public information that may be more informative, or at least more accessible. Journalists are conspicuously prone to this bias. For instance, as Brexit blogger Richard North has lamented repeatedly, UK journalists would breathlessly hype the latest leaks of government planning documents revealing the extent of adjustments that would be needed for phytosanitary checks at the border, for instance, or aviation, where the same information had been available for a year in official planning documents on the European Commission website. This psychological bias was famously exploited by WWII British intelligence operatives in Operation Mincemeat, where they dropped a corpse stuffed with fake plans for an invasion at Calais into the sea, where they knew it would wind up on the shore in Spain. They knew that the Germans would take the information much more seriously if they thought they had found it covertly. In my own experience of undergraduate admissions at Oxford I have found it striking the extent to which people consider what they have seen in a half-hour interview to be the deep truth about a candidate, outweighing the evidence of examinations and teacher evaluations.

Which brings us to Donald Trump, who has been accused of colluding with foreign governments to defame his political opponents. He has done his collusion both in private and in public. He famously announced in a speech during the 2016 election campaign, “Russia, if you’re listening, I hope you’re able to find the 30,000 emails that are missing. I think you will probably be rewarded mightily by our press.” And just the other day he said “I would think that if [the Ukrainean government] were honest about it, they’d start a major investigation into the Bidens. It’s a very simple answer. They should investigate the Bidens because how does a company that’s newly formed—and all these companies—and by the way, likewise, China should start an investigation into the Bidens because what happened in China is just about as bad as what happened with Ukraine.”

It seems pretty obvious. But no, that’s public information. Trump has dismissed his appeal to Russia as “a joke”, and just yesterday Senator Marco Rubio contended that the fact that the appeal to China was so blatant and public shows that it probably wasn’t “real”, that Trump was “just needling the press knowing that you guys are going to get outraged by it.” The private information is, of course, being kept private, and there seems to be a process by which formerly shocking secrets are moved into the public sphere gradually, so that they slide imperceptibly from being “shocking if true” to “well-known, hence uninteresting”.

I am reminded of the epistemological conundrum posed by the Weimar-era German cabaret song, “Ich möcht’ so gern wissen, ob sich die Fische küssen”:

Ich möcht’ so gerne wissen
Ob sich die Fische küssen –
Unterm Wasser sieht man’s nicht
Na, und überm Wasser tun sie’s nicht!

I would so like to know
if fish sometimes kiss.
Underwater we can’t see it.
And out of the water they never do it.