David McKenzie from the World Bank:
This evidence is thus consistent with the view that blogging helps build prestige and recognition in the profession, with bloggers being more likely to be admired or respected than other academics of similar (or in many cases better) publication records. This is of course only a correlation, and there are several caveats to consider. First, to the extent that blogging serves to increase the RePEc ratings by increasing own downloads (as seen in our previous post) and citations, the observed correlation will be a lower bound on the causal impact of blogging. However, if bloggers are also more likely to be engaged in other activities of a public intellectual, such as media appearances, writing books etc., and if these don’t all arise directly as a result of blogging, the estimates will conflate the impact of blogging with the impacts of these other activities, thereby overstating the impact of blogs. Nevertheless, given the large magnitude of the coefficient observed, it does not seem likely that all of the observed impact of blogging just reflects omitted variables, and therefore we view this evidence as strongly suggesting that blogging increases the influence, respect, or public image of the blogger.
Look at all of those potential lurking variables they’ve identified.