The NBC News Political Unit and msnbc.com created the Voter Confidence Index as a way to measure the level of confidence the American electorate has in the president and his party at a given moment. The VCI also demonstrates how that level correlates to previous election results.
To create the index, we used a combination of three questions commonly asked in national polls — the president’s job approval rating, the direction of the country, and the so-called generic congressional ballot (which tracks voter preference between parties rather than individual candidates). There are other questions that can measure a level of confidence, but these three are widely recognized as key barometers.
In the VCI, a positive (+) measurement is generally a good sign for the president’s party while a negative number (-) is not.
To provide historical context, our pollsters calculated the national average of those same indicators as they existed prior to the midterm elections for every president dating back to Gerald Ford.
The results, most of the time, show that the lower the VCI number, the more poorly the president’s party did at the polls.
This does not always hold true. There are other mitigating factors in some circumstances, but the aggregate number derived from the three questions above captures the climate of the country at a given moment in time.
The VCI is not meant to be predictive of any specific outcome, rather it serves to offer a frame of reference for how the mood of the country can correspond to some midterm election results.
How is the VCI calculated?
We give equal weight to all three questions. We take the difference between two sets of numbers in each question and add them up.
For example, if 45 percent of people approve of the job the president is doing and 50 percent disapprove, then that’s -5. If just 30 percent of the county believe the country is headed in the right direction, but 60 percent think it’s off on the wrong track, then that’s -30.
And if 45 percent prefer a Republican-controlled Congress and 40 percent prefer a Democratic-controlled one, then that’s -5 for the president’s party. That would give a grand total VCI of -40.
Because not every poll asks all three questions, we took the average of the polls on each question, and combined those averages for a total VCI.
Which polls did you choose and why?
There are lots of polls out there and there is also plenty of disagreement in the statistical community about what constitutes a good poll or a bad poll. The NBC News standard is to generally use polls that are done with live callers, not ones that are automated.
For the VCI, we chose to use the best known and most often conducted live-caller national polls: NBC News/Wall Street Journal, ABC News/Washington Post, CBS News/New York Times, Fox News/Opinion Dynamics, CNN/Opinion Research, Pew Research, USA Today/Gallup, Ipsos (including AP, Reuters, McClatchy), AP/GFK, Bloomberg/Selzer, and Newsweek.