Which factors most strongly impact voter turnout in the U.S.?

Question

Empirically, which factors most strongly impact voter turnout in the U.S.?

Are they the same for all political parties?

Clarification: I am not asking if one political party has greater turnout than another on average (this is true but not the question).

I am asking on a factor by factor basis if there is a differential effect (e.g. due to election day weather, age, recent news events, voter registration rules, photo-ID rules, mail in v. in person ballots, safe v. close districts, closing contested top of ticket races or ballot issues, etc.).

Answer 1

This seems rather broad. Here's some material to get you started:

• Early voting associated with lower turnout.

  Voters are less motivated to cast ballots because early voting has the effect of “dissipating the energy of Election Day over a longer period of time….[S]ocial pressure is less evident, guidance on how or where to vote is less handy, and the prospect of social interactions at the polls is decreased,” they wrote.

• [N]ew study suggests voter ID laws have little to no impact on minority voter turnout.

• The Weather & Voter Turn Out. Rain and snow depress voter turnout, especially rain. Partisans are affected less than independent voters. At the time of the study, this favored Republicans because independents were Democrat leaning. The effect is relatively small regardless, .8% per inch of rain or .5% per inch of snow. Places where snow is common have no effect from snow.
• Increased polarization in politics reduces voter turnout.
• Voter turnout and district-level competitiveness in mixed-member electoral systems.

  The relative importance of these components differs between mixed-member proportional (MMP) and mixed-member majoritarian (MMM) systems. I argue that, due to this difference, the impact of district-level competitiveness on turnout is stronger in MMM than in MMP. An analysis of district-level electoral data from four countries confirms this hypothesis.

• The Effects of Ballot Initiatives on Voter Turnout in the United States.

  Using pooled time series data for the 50 states over a 26-year period (1970-1996), we find that the presence and usage of the initiative process is associated with higher voter turnout in both presidential and midterm elections. The disparity in turnout rates between initiative and noninitiative states has been increasing over time, estimated at 7% to 9% higher in midterm and 3% to 4.5% higher in presidential elections in the 1990s.

• Will Vote-by-Mail Elections Increase Turnout ?

  • Voting by mail does not increase turnout in presidential and gubernatorial general elections. In fact, turnout was 2.6 to 2.9 percentage points lower in mail ballot precincts, according to our analysis of two general elections held in representative samples of 18 and 9 counties.
  • Voters who cast their ballots by mail in general elections are more likely to skip downballot races, another finding that runs counter to the expectations of vote-by-mail advocates.
  • However, voting by mail appeared to bring an average 7.6 percentage point turnout increase in local special elections, which have much lower participation rates overall. This finding is based on recent elections held in three counties.

• Electoral Competitiveness.

  One of the most important factors is the competitiveness of the presidential election in each state. Overall, 66% of eligible voters turned out to the polls in the nation's 12 most competitive states in 2012, but only 57% did in the nation's 39 other states (including the District of Columbia).

• Partisan Effects of Voter Turnout in Senatorial and Gubernatorial Elections.

  [...] since 1965 the overall relationship between turnout and partisan outcomes has been insignificant. [...] In the South, which we analyze only since 1966, higher turnout helped Republicans until 1990, but in 1990-94 the effect became pro-Democratic.