The preferred turnout rates are those calculated with the voting-eligible population as the denominator. The voting-eligible population (VEP) represents an estimate of persons eligible to vote regardless of voter registration status in an election and is constructed by modifying the voting-age population (VAP), by components reported in the right-most columns (scroll right in the spreadsheet).
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Direct link to spreadsheet.
The denominator data reflect the July 1, 2010 and July 1, 2011 Census Bureau voting-age population estimates interpolated to Nov. 2010, non-citizen estimates from the 2010 and 2011 American Community Surveys interpolated to Nov. 2010, the year-end 2010 DOJ prison report and the year-end 2010 DOJ probation and parole report. Starting in 2010, the citizen prison population is reported. Note, a '0' indicates that either a state does not disfranchise a class of felons or the state does not incarcerate felons within their borders. See The Sentencing Project for more information. The overseas eligible estimate is calculated from 2008 overseas citizen estimates provided by the Federal Voting Assistance Program.
For total ballots cast, I use the higher of a state's report of total ballots cast to the U.S. Election Assistance Commission for their 2010 Election Day Survey, or -- if it exists -- a higher number reported on official state websites or canvass reports. The discrepancy may be due to a number of factors, including: a state using vote history from a voter file that has undergone purging between the election and the report to the EAC or incomplete or erroneous reporting from local jurisdictions to the state in the course of the 2010 Election Day Survey. I choose not to report total ballots cast for Mississippi because the state did not report total ballots cast independently of the EAC, and their reported number to the EAC was less than the vote for highest office. For the national total ballots cast, I impute Mississippi's total ballots cast from the ratio of total ballots cast to vote for highest office for all other states, and apply this ratio the Mississippi's vote for highest office.