Monday, February 12, 2007

Seth's Blog has an interesting thought about causality and correlation.


I shed an invisible tear whenever I hear “correlation does not imply causation” which the otherwise excellent swivel (a website about correlations) emphasizes. Of course, there’s truth to it. It saddens me because:

  • It’s dismissive. It is often used to dismiss data from which something can be learned. The life-saving notion that smoking causes lung cancer was almost entirely built on correlations. For too long, these correlations were dismissed.
  • It’s misleading. In real life, nothing unfailingly implies causation. In my experience, every data set has more than one interpretation. To “imply” causation requires diverse approaches and correlations are often among them.
  • It’s a missed opportunity — namely, an opportunity to make a more nuanced statement about what we can learn from the data.
  • It’s dogmatic (see “Jane Jacobs on Scientific Method”). Some correlations, such as those from “natural experiments,” imply causation much more than others. I suspect it does more harm than good to lump all of them together.

  • In some sense I feel to agree to it. In some other I am in deep disagreement. Maybe we have gone from a correlation implies causality view to any correlations is not indication of causality. Economics has gone so far that Freaking economists are popular because are able to find examples in which causality is pointing in the opposite direction than correlations seem to imply.

    My sense is that decision theory may be able to help here. What if the correlation between smoking and lung cancer is actually causal? If we are wrong, that is confounding factors are at play, we may have sent bankrupt a few cigarettes companies. But it the relation is causal, as it is, we may have saved a lot of people.

    Experiments (in social sciences especially) should be left to case where benefit and costs of misinterpration balance themselves out.

    Tuesday, February 6, 2007

    Tuesday, January 30, 2007

    I am a statistician and when I look at the data...

    I am a statistician and when I look at the data, I have to say, there is something there.......

    This is how an ABC special on Extra-sensory perception [ESP] begins. There are psychics and politicians; there's the CIA and some statistics.

    Entertaining....... Get the video here

    Sunday, January 28, 2007

    Job Opportunity for Graduate Students

    I do not know who is running this site. But graduate students are always starving and they should not pass on money. Check this job offer. It seems they pay grad students for (short) reviewing papers.

    Thursday, January 25, 2007

    Interesting Seminar here at UCI

    The Department of Statistics here at UCI is having Peter Grünwald for a talk on Wednesday, January 31st. His research seems very interesting.

    Here the abstract:
    We show that forms of Bayesian learning that are often applied to classification problems can be *statistically inconsistent* when the model is wrong . More precisely, we present a family ('model') M of probability distributions, a distribution P outside M and a Bayesian prior distribution on M, such that - M contains a distribution Q within a small distance \delta from P. Nevertheless: - when data are sampled according to P, then, no matter how many data are observed, the Bayesian posterior puts nearly all its mass on distributions that are at a distance from P that is much larger than \delta. The classifier based on the Bayesian posterior can perform substantially worse than random guessing, no matter how many data are observed, even though the classifier based on Q performs much better than random guessing. The result holds for a variety of distance functions, including the KL (relative entropy) divergence.
    Misspecification themes are usually overlooked by the Bayesian statistical literature and it could not be differently. As long as one is concerned with actions to be taken and these action are taken with respect to the likelihood principle misspecification is noting more than a nuisance. Clearly the paper above add a (welcome) frequentist perspective.

    I am looking forward listening what Peter has to say.


    Wednesday, January 24, 2007

    iPods set the tempo in currency

    The Economist's BigMac index has had his fortune as informal way of measuring the purchasing power parity (PPP) between two currencies.

    Now
    Commonwealth Securities has launched an iPod index, based on the cost of the 2 gigabyte iPod Nano player as a way of showing if a currency is overvalued. BBC has a report on it.

    P.S.: If you plan to buy a iPod and you leave up north you should head your way into Canada.

    Graph your way into the new millenium

    This graph is very interesting. It plots income per capita for many countries over-time.