150,000 or bust
By Chris Larimer, Associate Professor, University of Northern Iowa
To say the results on Monday night will hinge on turnout is to state the obvious. But a closer look at the numbers reveals just how important overall turnout will be to the results, particularly the campaigns of Donald Trump and Bernie Sanders.
Using data maintained by George Washington University and the Iowa Secretary of State’s website, and as reported by Dennis Goldford of Drake University, recent turnout at the caucuses is not particularly impressive.
For the Democrats, the average turnout the last three competitive caucuses (2000, 2004, and 2008) was 141,654, or an average of 24.6 percent of active registered Democrats in the state. But there is considerable variation here. In 2000, 61,000 Democrats (or 11 percent) caucused in the race between Al Gore and Bill Bradley, while in 2008 nearly 240,000 (or 40 percent) Democrats turned out to caucus.
For the Republicans, for the last three competitive caucuses (2000, 2008, and 2012), there was less variation. Turnout averaged approximately 110,000 Republicans, for an average turnout rate of 18.5 percent, ranging from 15 percent in 2000 to 20 percent in 2012.
This raises two questions: Can Democrats realistically expect to replicate 2008? And, will this be a breakout year for the Republicans like 2008 was for the Democrats?
Mobilizing first-time caucus-goers is not easy, but as reported by Andrew Tartar on Bloomberg Politics, both the Donald Trump and Bernie Sanders campaigns are depending on it. While the polls in Iowa are tight, there are clear splits between first-time caucus-goers and those with caucus experience. While Trump and Sanders have double digit leads among “first-time participants,” they trail among those who have caucused before (Quinnipiac University poll).
Put another way, record turnout on caucus night would seemingly be to the benefit of Trump and Sanders.
What would record turnout in Iowa look like?
A number two standard deviations away from the mean is considered statistically significant. As of January 4, 2016, there were 584,111 active registered Democrats in the state and 612,112 active registered Republicans.
A two standard deviation increase for Republicans equates to a 6 percentage point increase over the mean, or 24.5 percent of active registered party member. Such an increase would mean just over 150,000 Republicans turning out on Monday night.
Given the variation in turnout among Democrats, a two standard deviation increase would be a 28 point increase over the mean, or 53.4 percent of Democrats. Since it is highly improbable that over 300,000 Democrats are going to show up on Monday, a more realistic prediction is probably something closer to turnout in 2004, as 2008 was extraordinary, and the polls suggest the enthusiasm in 2008 is simply not there in 2016. So, a three percentage point increase over 2004, or 26.3 percent, would be 153,738 Democrats caucusing on Monday night.
So, if you are looking for a number to watch on Monday night, focus on 150,000. If turnout for either party is significantly greater than this, chances are that one of the “outsider” candidates had a good night by effectively mobilizing first-time caucus-goers.