Health: how to avoid lazy thinking

When hundreds of Californians invaded the state capitol last week to demand the right not to vaccinate their kids, they were playing out a very modern conflict: science versus belief systems. Scientists tell parents that vaccinations are safe. But many parents prefer to trust their gut instinct that they're not safe. This dialogue of the deaf is becoming the norm. Increasingly, people make their own decisions on health and diet, instead of outsourcing them to scientists, doctors or governments.

If you want to change people's behaviour, don't recite science at them, says Alan Dangour, nutritionist at the London School of Hygiene and Tropical Medicine (LSHTM). Rather, to nudge people to better decisions, we need to understand how they decide. Behavioural economics has identified cognitive biases that influence our decisions about money. Here are some biases and misjudgments that shape decisions on health and diet:

When faced with complex problems, people often resort to a heuristic: a pragmatic, simplified mental shortcut. A common shortcut is to use labels such as "natural", "organic", "local" or "homeopathic" as proxies for healthy. Conversely, "artificial" gets equated with unhealthy. This heuristic appeals partly because it relies on words. Not everyone understands science but we all know language.

Sometimes, natural actually is good. The World Health Organisation announced last month that the world's most common weedkiller, glyphosate, can probably cause cancer. But often natural isn't good. For instance, homeopathy is ineffective for treating any medical condition, concluded Australia's National Health and Medical Research Council last month, echoing a report for Britain's House of Commons in 2010.

Likewise, "natural" organic foods aren't more nutritious than other foods, said researchers from the LSHTM, after reviewing 50 years of studies. A Stanford analysis of 237 studies concurred.

In fact, as Eula Biss explains in her book On Immunity, any single study in medicine is meaningless. To quote medical researcher John Ioannidis: "Most published research findings are false." A single study might have been small, poorly conducted or produce findings that are due simply to chance. "What matters," says Ioannidis, "is the totality of evidence." That's why the gold standard of medical research is the meta-study, such as the ones cited above on organic food, which aggregate previous research on a topic. Nonetheless anti-vaccinators still cite one now-retracted study of 12 children, published by Andrew Wakefield and others in 1998, which suggested that vaccinating children might cause autism.

People seize on single studies because we are bad at weighing quantities. We struggle to distinguish between "a little" and "lots". That's also why people panic when "traces" of "toxins" show up in a product - traces of mercury in vaccines, for instance. But quantity is crucial. Biss quotes a toxicologists' adage: "The dose makes the poison."

This religious notion survives in today's "detox diets", which often entail forswearing everything except selected "natural" products such as juices. In fact, "sinful" things such as wine, chocolate and coffee (a rare legal, mind-altering, performance-enhancing drug) are healthy in small quantities.

Our main source of information on health today is Google. However, you can find anything online, and most people gravitate to websites that confirm their beliefs.

People like certainty. In health, that's rarely available. Authorities sometimes change their minds: for instance, the US government is expected to announce soon that high-cholesterol foods are OK after all.

Instead of seeking certainty, we should make decisions on the balance of probability: vaccinating your kids is very probably smart. But probability feels too ambiguous to be reassuring.

People fret about terrorists, sharks, Ebola and plane crashes because of the availability heuristic. The more available a piece of information is to the memory - a terrorist attack, say - the more likely it is to influence our decisions. In fact, terrorism kills fewer people than sitting at a desk.

Smokers know that smoking is addictive and lethal. But they tend to believe it will only enslave and kill other smokers, says Jody Sindelar, professor at the Yale School of Public Health. In general, people downplay their unhealthy habits, preferring instead to blame disease on factors beyond their control: their genes or environmental factors such as mobile phones or radiation. You can see why.

We value the present above the future. The best time to quit smoking is therefore always tomorrow, says Sindelar.

Scientists and governments need to change tack. Instead of bombarding people with science, they should design policies that use our cognitive biases. One obvious technique is advertising. A gorgeous ad showing a mother cuddling a baby who is being vaccinated might be worth 10,000 scientific studies. Sindelar suggests other methods:

? Reminders: on sunny days, send people messages suggesting they put on sunscreen.

? Pre-commitments: encourage people to bet that they will lose specific amounts of weight.

? Financial incentives: pay people to give up smoking.

These nudges could do more than scientific findings to change behaviour. In today's low-trust world, science is in the doghouse with most other authorities.

[email protected]; Twitter @KuperSimon

Illustration by Andre Carrilho

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