The Hidden Half

The Unseen Forces that Influence Everything

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I put this book on the get-at-library list after listening to the episode of the Econtalk podcast where the author, Michael Blastland, was interviewed by host Russ Roberts. I'm somewhat embarrassed to admit that I didn't recognize Blastland as the co-author of the excellent book The Norm Chronicles, which I read back in 2014. This book is really good too. Blastland is a journalist (but a smart one), and his prose is lively and accessible.

Here, he takes a hard look at the concept of "all other things being equal". A concept so ancient, it's sometimes expressed in Latin: ceteris paribus. (This page says that Cicero used it.) Although most common explicit use of the phrase seems to be in economics, the concept underlies a lot of science. And for that matter, a lot of life.

The problem being: how can you assume "other things being equal" when they so often are not?

Blastland opens with an unexpected example: the marmorkreb, a species of crayfish. They are parthenogenetic, with all offspring being genetically equal females to their mother. A few years ago, German researchers decided to raise a batch of marmorkrebs with identical environments as well. And yet, their marmorkrebs defied their genes and upbringing, and became unexpectedly diverse. Their size varied greatly, as did their coloration. They socialized with other marmorkrebs differently; they had different lifetimes; they had different eating behaviors; …

It's almost as if they were individuals, not simply mass-produced clone crayfish. And if you can't assume ceteris paribus with a bunch of clones, how can you assume it elsewhere?

Blastland answers: you often can't, and you shouldn't. Simple mental models of how things "should" work are often correct. But just as often (about half the time?) they fail, because of underlying complexities and confounding details that you didn't consider.

From there, Blastland takes a wide-ranging tour of how that works (or doesn't). Many stories, most interesting. There's (for example) sinful boxer Mike Tyson, compared and contrasted with his sainted surgeon brother Rodney. Tons of research studies that turned out to be irreproducible.

There's way too much to try to summarize, but I found one issue Blastland raises particularly interesting, and it brings in his Norm Chronicles co-author, David Spiegelhalter: studies of "risky behavior" based on large sample populations can be (and often are) reported misleadingly. The semi-amusing example was from the Lancet where the well-documented result was that there is "no safe level" of alcohol consumption. Even one drink per day raised your risk of developing a serious alcohol-related health problem. And the article suggested that public health institutions should “consider recommendations for abstention”.

Let's swing over to Spiegelhalter's Medium article that Blastlad cites:

Let’s consider one drink a day (10g, 1.25 UK units) compared to none, for which the authors estimated an extra 4 (918–914) in 100,000 people would experience a (serious) alcohol-related condition.

That means, to experience one extra problem, 25,000 people need to drink 10g alcohol a day for a year, that’s 3,650g a year each.

To put this in perspective, a standard 70cl bottle of gin contains 224 g of alcohol, so 3,650g a year is equivalent to around 16 bottles of gin per person. That’s a total of 400,000 bottles of gin among 25,000 people, being associated with one extra health problem. Which indicates a rather low level of harm in these occasional drinkers.

In short: yes, drinking alcohol is risky. But on the individual level the additional risk is small. To repeat: in that population of 100,000, all imbibing one drink per day, four of them would develop a health problem due to their booze consumption.

Spiegelhalter comments:

But claiming there is no ‘safe’ level does not seem an argument for abstention. There is no safe level of driving, but government do not recommend that people avoid driving.

Come to think of it, there is no safe level of living, but nobody would recommend abstention.

It's amusing, sure. But note that this type of research is used to advocate for "public health" measures including taxes, regulations, and prohibitions. It's all fun and games until somebody gets coerced.