Somewhat belatedly, I would add another item to the list of studies on the above topic (requested by Ron Mitchell). This one deals with regime "repressiveness" (and other factors) rather than democracy, per se, but may be the grandparent of 'em all. It uses the 1992 Dietz and Kalof data.
J Timmons Roberts, "Predicting Participation in Environmental Treaties: A World System Analysis" Sociological Inquiry, 66, Feb 1996.
