Turnout is typically calculated as the number of votes cast divided by the voting-age population (VAP) which is estimated by the Census Bureau as the number of residents in a jurisdiction eighteen years and older. Note that VAP is an estimate since it includes persons ineligible to vote, mainly non-citizens and ineligible felons, and excludes overseas eligible voters. Primary election turnout estimates here combine in the numerator votes cast in both the Democratic and Republican primaries. National Turnout as a percentage of VAP is from the Federal Election Commission at http://www.fec.gov, accessed 1 July 2004. Texas turnout figures are from the Texas Secretary of State athttp://www.sos.state.tx.us/elections/historical/70-92.shtml, accessed 2 January 2013.

For the 2004, 2008 and 2012 presidential elections, national turnout as a percentage of VAP comes from the United States Elections Project, George Mason University, http://elections.gmu.edu, January 2, 2013.