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Last week, I went to the Econometrics seminar of Montréal, at UdM, where Alfred Galichon was giving a great talk on marriage market. Alfred is a former colleague (from France), a co-author, an amazing researcher, and above all, a friend of mine. And he has always be supportive about my blogging activities. So while we were having lunch, after the seminar, Alfred mentioned my blogging activity to the other researchers. I should say researchers in Econometrics (yes, with a capital E, since it is a Science, as mention in an old paper by David Hendry by the end of the 70's). Usually, when I am involved in this kind of meeting, I start with some apologies, explaining that I do like theoretical econometrics (if not, I would not come to the seminar), but I do like my freakonometrics activity. I do like to use econometrics (or statistical techniques) to figure out (at least to try) why some things works the way they do. I try to find data, and then try to briefly analyze them to answer some simple questions. Or sometime, I just run simulations to answer more theoretical questions (or at least to give clues).But above all, I like the fact that blogging gives me the opportunity to interact with people I would never meet without this activity. For instance, last May, I was discussing (on Twitter) with @coulmont, @joelgombin and @imparibus about elections in France. Then @coulmont asked me "yes, everyone knows that there should be some ecological fallacies behind my interpretation, but I am not so sure since I have data with a small granularity. As an econometrician, what do you think ?" Usually, I hate having a label, like "... I ask you since you're a mathematician", or "as an economist, what do you think of...". Usually, when people ask me economic questions, I just claim being a mathematician, and vice-versa. But here, I even put on the front of my blog the word "econometrics" (more or less). So here, I could not escape... And the truth is, that while I was a student, I never heard anything about this "ecological fallacy". Neither did I as a researcher (even if I have been reading hundreds of econometric articles, theoretical and applied). Neither did I as a professor (even if I have been teaching econometrics for almost ten years, and I have read dozens textbooks to write notes and handouts). How comes ? How come researchers in sociology and in political sciences know things in econometrics that I have never heard about ?The main reason - from my understanding - is the following: if everyone talks about "interdisciplinarity" no one (perhaps a few) is really willing to pay the price of working on different (not to say many) areas. I tried, and trust me, I found it difficult. It is difficult to publish a paper in a climate journal when you're not specialist in climate (and you just want to give your opinion as a statistician). It is difficult to assume that you might waste weeks (not to say months) reading articles in geophysics if you want to know more about earthquakes risks, going to seminars, etc. Research is clearly a club ("club" as defined in Buchanan (1965)) story.This week, I planned to go to some journal club in biology and physics, at McGill (kindly, a colleague there invited me, but we got a time misunderstanding)... this has nothing to do with my teaching, nor with my research activities. But I might learn something ! Yes, I do claim that I am paid just to have fun, to read stuff that I do find interesting, trying to understand the details of a proof, trying to understand how data were obtained. In most cases, it might (and should) be a complete waste of time, since I will not publish anything (anything serious, published in some peer reviewed journal) on that topic... but should I really care ? As I explained earlier (in French), I do also claim that I have a moral obligation to return everything I have seen, heard, read. And since I am not a big fan of lectures (and that I do not think I have skills for that) I cannot give my opinion, neither on economics facts (as @adelaigue or @obouba might do on their blogs) or on science results (as @tomroud does). But I think I can help on modeling and computational issues. My point being: never trust what you read (even on my blog) but please, try to do it yourself! You read that "90% of French executive think about expatriation" (as mentioned here)? Then try to find some data that should confront that statement. And see if you come up with the same conclusion... And since it might be a bit technical sometimes, here are some lines of code, to do it on your own... Academics have a legitimacy when they give their opinions on technical issues. At least they can provide with a list of reference everyone should read to get an overview of the topic. But academics can also help people read graphs, or data. To give them "numeracy" (or a culture in numbers) necessary to understand complex issues.To conclude, I should mention that I understood what this "ecological fallacy" was from  Thomsen (1987) and many more documents could be found on Soren Thomsen's page http://www.mit.ps.au.dk/srt/. But I got most of the information I was looking for from a great statistician, who happens to be also an amazing blogger: Andrew Gelman (see http://andrewgelman.com/). I will probably write a post someday about this, since I found the question extremely interesting, and important.