This is the question:

Calculate the percentage of voters who voted for either candidate. Be careful to select the proper reference population in the denominator. Justify your calculation.

This is the data:

You are given the absolute counts of votes for Trump (TRUMPVOT16), Clinton (CLINTONVOT) and others[1] (OTHERVOT16), as well as the number of persons 18 years and older[2] (POP18PLUS), number of registered voters[3] (REGVOT16) and the turnout rate[4] (TURNOUT16).

[1] Besides the two main candidates, the electorate also has had a choice to vote for independent candidates and Libertarians. Only a very small number of voters in each county has chosen these alternatives.

[2] Note that not all persons 18 years and older qualify to vote; for instance, because some are not U.S. citizens.

[3] In Texas, voters need to register in order to be eligible to vote. This does not imply that all registered voters will participate in an election.

[4] The turnout percentage is that proportion of registered voters who participate in an election.

You are given the absolute counts of votes for Trump (TRUMPVOT16), Clinton (CLINTONVOT) and others[1] (OTHERVOT16), as well as the number of persons 18 years and older[2] (POP18PLUS), number of registered voters[3] (REGVOT16) and the turnout rate[4] (TURNOUT16).

[1] Besides the two main candidates, the electorate also has had a choice to vote for independent candidates and Libertarians. Only a very small number of voters in each county has chosen these alternatives.

[2] Note that not all persons 18 years and older qualify to vote; for instance, because some are not U.S. citizens.

[3] In Texas, voters need to register in order to be eligible to vote. This does not imply that all registered voters will participate in an election.

[4] The turnout percentage is that proportion of registered voters who participate in an election.