From an upcoming paper by Duke professor Nicholas Carnes,who studied the connection between the occupational backgrounds of members of Congress from 1901 to 1996 and their voting behavior:PDF
With the exception of a modest increase in the percentage of representatives classified as career politicians in the early 1980s and a corresponding drop in the proportion of lawyers, the occupational makeup of the House changed surprisingly little during the 20th century (despite seismic changes in the composition of the American workforce). For most of the last hundred years, between one and two thirds of representatives were lawyers.
HT: NYT
