Posts filed under Evidence (90)

Philosophers have argued about whether it’s even conceivable to have pain without the physical sensation. According to 3News (and other media outlets worldwide), University of Chicago neuroscientists don’t have a problem with this:

Mathematics can be difficult, and a new study shows even thinking about doing it can physically hurt.

Of course, that’s not quite what the study found (and credit to 3News for linking), though it does seem to be what the researchers said they found. The study was in people with ‘high levels of math anxiety’ and the abstract says

We show that, when anticipating an upcoming math-task, the higher one’s math anxiety, the more one increases activity in regions associated with visceral threat detection, and often the experience of pain itself (bilateral dorso-posterior insula).

That is, some of the parts of the brain that are active during pain or threat were also active when anticipating a maths task, even though there was no actual pain reported.

A simpler explanation might be that if you’re scared of maths, then your brain looks as if you’re scared of something.  Although the researchers don’t believe this, they do actually concede it is an alternative explanation in the discussion section of the paper

the INSp activity we found could be reflective of something else. For example, it has been suggested that INSp activity is not so much reflective of nocioception, but rather reflects detection of events that are salient for (e.g., threatening to) bodily integrity, regardless of the input sensory modality

(via)

The occasion is Nate Silver and the data-based predictions of the US election, but Mark Coddington raises a much more general point about the difference between ways of knowing things in journalism and science.

The journalistic norm of objectivity is more than just a careful neutrality or attempt to appear unbiased; for journalists, it’s the grounds on which they claim the authority to describe reality to us. And the authority of objectivity is rooted in a particular process.

But science finds things out differently, so journalists and scientists have difficulty communicating with each other.  In political journalism, the journalist gets access to insider information from multiple sources, cross-checks it, evaluates it for reliability, and tells us things we didn’t know.  In data-based journalism there aren’t inside secrets. Anyone could put together these information sources, and quite a few people did.  It doesn’t take any of the skills and judgment that journalists learn; it takes different skills and different sorts of judgment.

TL;DR: Political journalists are skeptical of Nate Silver because they don’t understand and don’t trust the means by which he knows what he knows. And they don’t understand it because it’s completely different from journalists have always known things, and how they’ve claimed authority to declare those things to the public.

Q:  Have you seen the headline: “Skipping breakfast makes you gain weight: study”?

A:  If that’s the one with the chocolate cupcake photo, yes.

Q:  Was this just another mouse study, or did they look at weight gain in people?

A: People, yes, but they didn’t measure weight gain.

Q: But doesn’t the headline say “makes you gain weight”?

A: Indeed.

Q: So what did they do?

A: They measured brain waves, and how much pasta lunch people ate. The people who skipped breakfast ate more.

Q: So it was a lab experiment.

A: You can’t really tell from the Herald story, which makes it sound as though the participants just chose whether or not to have breakfast, but yes.  If you look at the BBC version, it says that the same people were measured twice, once when they had breakfast and once when they didn’t.

Q: And how much more lunch did they eat when they didn’t eat breakfast?

A: An average of 250 calories more.

Q: How does that compare to how much they would have eaten at breakfast?

A:  There were brain waves, as well.

Q: How many calories would the participants have eaten at breakfast?

A: The part of the brain thought to be involved in “food appeal”, the orbitofrontal cortex, became more active on an empty stomach.

Q: Are you avoiding the question about breakfast?

A: Why would you think that?  The breakfast was 730 calories.  But the MRI imaging showed that fasting made people hungrier

Q: Isn’t 730 more than 250?

A: Comments like that are why people hate statisticians.

That’s how Ben Goldacre described the process of criticism and debate that’s fundamental to science, at a TED talk last year.  At this time of year we expose a lot of innocent young students to this process: yesterday it was the turn of statistical consulting course, next month it’s BSc(Hons) and MSc research projects, and then the PhD students.

Here’s Ben Goldacre’s whole talk

An interesting post on how media reporting of risk could actually make us less safe. (via)

Any binary decision requires us to consider both the probability of getting it right and the consequences of getting it wrong.  Many legal systems have traditionally felt that wrongful convictions are worse than wrongful acquittals, and this forms part of the support for the presumption of innocence.

In other areas of the law, the incentives are different.  In automated detection of unauthorized copying, and resulting ‘takedown’ notices under laws such as the US DMCA, there is effectively no risk to the copyright holder from false positives, so there is not much incentive to avoid them.

An interesting example (via the far-from-unbiased BoingBoing) is this takedown notice, one of the stream routinely posted by Google at ChillingEffects.  The first few pages just show torrent sites that posted unauthorised copies of MS Office and deserve what’s coming to them, but if you scroll down to Copyright Claim #2, it starts to look different: (more…)

The Cochrane Collaboration are holding their annual conference in Auckland starting on Sunday.  They are a decentralised, grassroots effort to collate and summarise all randomised clinical trials, to make sure that the information isn’t buried, but is available to clinicians and patients.  The online Cochrane Library of Systematic Reviews is available free to anyone in New Zealand, thanks to funding from the DHBs and the Ministry of Health.  As with many organisations, they award a variety of prizes in their field of work.  In contrast to many organizations, one of the prizes is awarded for the best criticism of the organization’s work.

Anyway, the conference is an excuse to link to a video by the Cambridge “Understanding Uncertainty” group.  They are working on animations to further improve the summaries of health findings from the Cochrane systematic reviews.

Stuff has a story pointing out that conspiracy theories go together:

If you think smoking doesn’t cause lung cancer, HIV doesn’t cause Aids or Nasa faked the Moon landing, you are also more likely to support free market economics and be sceptical about climate change.

An apparently stronger version of this was demonstrated in a study published in January this year,

The Herald  is at least showing some scepticism about Italian-style patisserie that is supposed to make you lose weight (they include green tea and guarana, ie, caffeine).  The manufacturer isn’t willing to give any numbers

But she said it was not possible to measure how much eating the treats would help boost the metabolism because ‘everyone is different’.

Of course, this is a pretty transparent excuse.  If the fact that everyone is different made measurements impossible, medical science would be in a bad way.  We can measure the average effect.  We can measure the variability in the effect.  We can measure the proportion of people helped.  And we do all these things.  For example,  we’ve known for years that angiotensin converting enzyme inhibitors reduce blood pressure on average by about 10mmHg.  More recently, some Sydney researchers reanalyzed the data from the randomized trials to look at how much person-to-person variation in effect there was, and found it was extremely small.

The story goes on to say

Registered public health nutritionist Charlotte Stirling-Reed said that consumers should always look for evidence before making purchases based on health claims.

John Key is quoted in the Herald as not understanding minimum unit pricing

Mr Key believed that if a minimum price were set, it would change the quality of alcohol that people drank, but not the amount.

“What typically happens is people move down the quality curve and still get access to alcohol.”

The point of minimum unit pricing, as opposed to increased excise rates, is precisely to stop this.  The idea is that there is a minimum retail price for a quantity of alcohol: the proposal here was $1.50 per standard drink, in the law recently passed in Scotland it is 50p, and in the Canadian province of Saskatchewan it is $2.25.  If the price of your currently-preferred adult beverage is raised by the law, everything ‘down the quality curve’ will also have its price raised to exactly the same level.

There are reasons why it might not work: the price elasticity of demand might be low or there might be too much black-market supply. Reasonable people could also believe the benefits aren’t worth the impact on moderate drinkers: eg, at $1.50 per 12g of alcohol most red wines (at 14% alcohol) would have to cost at least $13.50 per bottle.  But, if anything, it would move people up the quality curve, not down.  That’s why it’s different from just raising excise rates.

You can read an analysis of the impact of the Saskatchewan policy, presented to the Scottish Parliament by a Canadian researcher: it seems to have reduced the quantity of alcohol drunk and also led people to drink lower-alcohol beverages.