Nathan Yau at Flowing Data links to this lovely analysis of average dissertation lengths at Minnesota. Here’s the key chart:

Two random thoughts about this. 1. History, as befits its reputation, really is a bit of an outlier in having long dissertations, with Anthropology a close second, and 2. Sociology has one of the widest boxes, probably reflecting the diversity of methods employed in the field (quant dissertations being short like econ, historical dissertations being long like history). Economics has one of the tightest boxes. All of which suggests that a tight page range is one (kind of silly) measure of disciplinary uniformity (of a sort, anyway).