December 26, 2010 § Leave a comment
From the FAQ on the website of the Equality Trust, an organisation founded by Billy Kerry, Richard Wilkinson, and Kate Pickett. The latter two are authors of the highly influential book The Spirit Level.
Correlation does not prove causality. What reasons are there for thinking that inequality is the cause of such a wide range of health and social problems?
To suggest that these relationships are causal does not involve a major departure from what we know already. Within countries we know that all the components of our Index of Health and Social Problems are strongly related to social status: the further down the social ladder the more common they become. The new part of the picture is simply that if you stretch out the social status differences all the problems related to social status become more common. Rather than postulating entirely new causal processes we are therefore only providing a bit more information about the relationships that have always been recognised.
People who have studied the graphs on this web site and in The Spirit Level carefully will have noticed that there is a clear tendency for countries which do badly on one outcome to do badly on others. We show evidence that 10 or 12 different problems tend to move together. That implies that they share an underlying cause. The association between inequality and our Index of Health and Social Problems is very close and no one has yet suggested an alternative.
Lastly, as the different chapters in our book show, many of the causal processes leading from inequality to the various health and social problems are already known. For example, the effects of social status on health have been demonstrated among monkeys in experiments which kept diet and material conditions the same while altering social status by moving animals into new groups and the effects of chronic stress on the immune and cardiovascular systems are increasingly well understood. Similarly, violence is more common in more unequal societies (where status competition is intensified) because it is so often triggered by people feeling looked down on, disrespected and humiliated.
December 25, 2010 § Leave a comment
Gerd Gigerenzer has produced the most challenging response to Kahneman and Tversky’s work on (quote-unquote) rationality as it relates to human judgement of uncertainty. In this series, I’ll work through Gigerenzer’s pop-sci books Calculated Risks and Gut Feelings and pick out bits I can apply to my thinking and teaching.
I’m not an absolutist who holds that nothing in the future is certain. It’s certain that the sun will rise tomorrow. Pedantic spiritualists and/or quantumists may argue that there is some non-zero probability that in the next few hours the sun will turn into a supermassive slice of cheesecake. Yet if the concept of certainty is to have any use, complement probabilities of the order of 10^(10^10) should be considered negligible. Certainty is best employed as an approximate concept—like approximately everything else.
Yet problem zero in statistical thinking is not understatement but overstatement of uncertainty. It’s not just undergrads that make this mistake. We pros know that our estimates are almost surely wrong, and append uncertainties to them. Yet we have a habit of assuming our quantification of uncertainty is exact, when in all but the simplest real-world problems, our chance model will be wrong. We should be more concerned with teaching students how the real world can deviate from our models that with teaching them when to divide by n and when to divide by n-1.
December 22, 2010 § 2 Comments
I’m starting this blog because I have little to show for too much time spend arguing about statistics on the Internet. The thing is, I think that arguing about statistics on the Internet can have a positive effect.
Frank Sulloway and Richie Zweigenhaft published a paper on the relationship between birth order and risk-taking among Major League Baseball players. In the past, when two (or more) brothers have made it to the majors, the younger brother is a bit more likely to have the higher rate of attempted steals in the family. Sulloway and Zweigenhaft were worried about the confounding effect of ability, so they controlled for birth order, comparing older brothers called up first to younger brothers called up first, and older brothers called up second to younger brothers called up second. Now the difference is huge (odds ratio 10.58).
Phil Birnbaum and his commentariat thought this was weird at best, and to me it seemed like a Type M error. To Sulloway and Zweigenhaft’s credit, they responded to the concerns raised. To me, though, the main concern—the weird control—isn’t convincingly dealt with. My thoughts are strewn across several comments on Phil’s blog. I’d like to edit them before reproducing them here. Maybe next week.
December 19, 2010 § Leave a comment
What if I told you that last week I predicted all eight winners of a round of the World Cup? And that instead of rankings or divination all I did was look up how many people in each team’s home country had a tiny parasite lurking in their amygdalas? Would you believe me? A decade ago, Discover Magazine concluded that parasites ruled the world, and now I’m going to try to tell you that, at the very least, parasites rule the World Cup…
If we set aside the qualifying rounds (in which teams can play to a draw) and focus on matches with a clear winner, the results are very compelling. In the knockout round of this year’s tournament, eight out of eight winners so far have been the teams whose countries had higher rates of Toxo infection. If we go back to the 2006 World Cup, seven out of eight knockout-round winners could be predicted by higher Toxo rates.