All data relating to state legislature seats held by the Democratic and Republican Parties were calculated from a data set collected originally by Walter Dean Burnham: “Partisan Division of American State Governments, 1834–1985”, Inter-University Consortium for Political and Social Research, Study No. 16.

Data for congressional elections between 1880 and 1932 in cities with populations of more than 200,000 (and used in Tables 3.6, 3.7, and 5.1) were calculated by the author from data presented in Congressional Quarterly's Guide to U.S. Elections, Third Edition, Washington, DC, Congressional Quarterly, 1994. The cities comprised all those in northern and Border states, but excluded those in the 11 southern states. Cities were included in the data for the first election following a U.S. Census that revealed the city now had a population of at least 200,000. The counties that formed a congressional district were checked, and districts were included in the data when it was clear that at least 50 per cent of the electorate of that district were residents of the county containing the city of 200,000. In the case of many states, the decision as to which districts should be included, and which omitted, was relatively straightforward. There were some “difficult cases”, however. A good example is New Jersey. Newark and Jersey City both warranted inclusion from 1912, but the state legislature drew district boundaries so that the cities were divided among several districts, and in no single district did those parts of the city included constitute a majority of the district.