|Vote-Share Equations: November 2014 Update|
Presidential and Congressional
Vote-Share Equations: November 2014 Update, discusses the
November 2014 update of the vote-share equations. Forecasts for
2016 are also made.
This discussion assumes that the paper,
Presidential and Congressional
Vote-Share Equations, American Journal of Political Science,
January 2009, 55-72, has been read.
Compute your own prediction: The following link allows you to compute your own predictions of the 2016 presidential and House elections. Compute your own predictions for 2016
Predictions: The current and past predictions of VP and VC using the economic forecasts from the US model are:
G P Z VP VC November 11, 2014 2.97 2.14 6 48.7 47.6 January 31, 2015 3.04 1.86 3 46.0 46.1 April 29, 2015 3.22 1.14 5 48.6 47.6 July 31, 2015 3.03 1.33 3 46.4 46.3 October 31, 2015 2.16 1.37 3 45.8 46.0 January 30, 2016 1.97 1.37 3 45.7 45.9 April 28, 2016 0.87 1.28 3 45.0 45.5VP is the Democratic share of the two-party presidential vote, and VC is the Democratic share of the two-party vote in the House. Click the above "Compute your own predictions for 2016" for the definitions of G, P, and Z.
April 28, 2016, comment: The forecast for G is now lower (0.87 versus 1.97 for the previous forecast), and so the predicted vote share for the Democrats is lower (45.0 for VP versus 45.7 for the previous forecast). The main message has not changed, however, and so there is nothing new to add to the previous comments below. The economy in terms of the growth rate of GDP is clearly not a plus for the Democrats in 2016. This could, of course, be trumped by other factors.
January 30, 2016, comment: The US model forecast dated January 30, 2016, is almost unchanged from the forecast dated October 31, 2015, and so the vote-share predictions are essentially unchanged. There is nothing new to add to the previous comments below.
October 31, 2015, comment: In the current NIPA data there are three good new quarters: 2014:2, 2014:3, and 2015:2. The US model forecast dated October 31, 2015, is predicting no more good news quarters, so Z is 3. G is down to 2.16 compared to 3.03 for the July 31, 2015, forecast. P is little changed. The lower G results in the prediction for VP falling from 46.4 to 45.8 and the prediction for VC falling from 46.3 to 46.0.
The October 31, 2015, forecast from the US model is close to the current consensus forecast (remember that G is per capita growth; the growth rate non per capita in the first three quarters of 2016 is 2.81 percent, which is close to consensus). If this turns out to be roughly the case, the Democrats are predicted to lose by a fairly large amount. See the earlier comments for more discussion.
July 31, 2015, comment: In the revised NIPA data that were released on July 30, 2015, 2013:3 is no longer a good news quarter, and so there have so far since 2013:1 been only two good news quarters: 2014:2 and 2014:3. The US model forecast dated July 31, 2015, is predicting one more good news quarters, 2016:3, compared to two in April 29, 2015, 2016:2 and 2016:3. So Z is down from 5 to 3. There is little change in G and P, but the fall in Z is important. The prediction for VP is down from 48.6 to 46.4, and the prediction for VC is down from 47.6 to 46.3.
A further comment about Z. As noted in the April 29, 2015, comment below, Z is sensitive to small changes in growth-rate predictions. I am using 0.65 percent as the rate of growth of population going forward, and if I used 0.66 instead, 2016:3 would no longer be a good news quarter. This would subtract a point from VP, making it 45.4 percent. Also as noted in the April 29, 2012, comment, the consensus forecast does not have any more good news quarters, so Z is two for it.
April 29, 2015, comment: The US model forecast dated April 29, 2015, is predicting two more good news quarters: 2016:2 and 2016:3. (There have so far been three: 2013:3, 2014:2, and 2014:3.) So Z is 5. G is little changed from the previous two forecasts, although P has been falling. The prediction for VP is now 48.6 percent, and the prediction for VC is 47.6 percent.
The US model forecast is more optimistic than the current consensus view. For example, the Survey of Professional Forecasters of the Philadelphia Fed has a predicted growth rate of 2.9 percent in 2016 (and about the same for the rest of 2015). Using a population growth rate of 0.75 percent, this is a per capita growth rate of 2.15 percent. So G is 2.15. Given this growth rate for the year, there are unlikely to be any good news quarters, so Z remains at 3. Assuming that P is, as for the US model, 1.14, this implies a prediction for VP of 45.9. (Use the "Compute your own predictions for 2016" link above and plug in 2.15, 1.14, and 3.) The current consensus economic view thus implies a fairly large loss for the Democrats.
A comment about Z. The US model forecast has predicted growth rates in the first three quarters of 2016 of 3.91, 4.02, and 3.97. Using 0.75 as the population growth rate, which is in line with recent rates, these are per capita growth rates of 3.16, 3.27, and 3.22. The cutoff for a good news quarter is 3.2, so two of these three are good news quarters. In fact, of course, these three rates are essentially the same. Each good news quarter is worth about one percentage point of vote share, so the vote prediction is somewhat sensitive to which side of the cutoff a growth rate is on. Historically the best fit is obtained using a cutoff of 3.2, but the fits for values near this are similar. This sensivity is not a problem using the current consensus economic forecast because the per capita growth rates are not near 3.2 percent, but for the US model forecasts one should be aware that the vote prediction is somewhat sensitive to the use of 3.2 as the cutoff.
January 31, 2015, comment: The US model forecast dated January 31, 2015, is not predicting any more good news quarters. There have been 3 so far (2013:3, 2014:2, and 2014:3). So Z is 3. In the previous forecast Z was 6. For the current economic forecast G is slightly larger and P is slighter smaller, both good for the Democrats, but the lower Z is bad. The net effect for VP, the two-party presidential vote share for the Democrats, is that it has fallen from 48.7 to 46.0. VC, the two-party vote share for the Democrats in the House, has fallen from 47.6 to 46.1. Conditional on the present forecasts of the economy, the two vote share equations are thus pessimistic about the Democrats chances in 2016.
November 11, 2014, comment: The economic forecasts from the US model dated October 30, 2014 are used for this prediction. The US model economic forecasts are fairly optimistic about the U.S. economy between now (November 2014) and the third quarter of 2016. Conditional on these economic forecasts, the prediction for VP is 48.7 and the prediction for VC is 47.6. So even with a fairly good economy, the Democrats' predicted shares are less than 50 percent. See the discussion of Table 6 on page 12 in the first paper linked above for alternative predictions.
Data for downloading:
Previous update papers:
Web site material for previous elections: