Thanks to Brad DeLong, who has collected some of my oldies from January 2016. Back then, I outlined how polling data and Republican party rules pointed clearly toward a Trump nomination.

Here at PEC we are ramping up slowly. In the top banner is a preview of the main product: a snapshot of state polls. It’s basically the same as previous years, a day-to-day snapshot of state polls for the general election. This year, I am also adding a November prediction.

Brief notes:

As longtime readers know, I use all available state polls to calculate an estimate of where the Presidential race stands on any given day. The methods are detailed here. Basically, I use the median and estimated uncertainty of each state’s recent polls to calculate a win probability. Then I calculate a compound probability distribution of all possible combinations (2.3 quadrillion of them) combined, which gives the histogram you see above. That is a snapshot of current conditions. As you can see, Hillary Clinton would win an election held today.

The Meta-Margin is defined as how far the Clinton-Trump margins in state polls would have to change, across the board, to create a perfect knife-edge race in which the median outcome is an electoral tie 269 EV to 269 EV. Today the Meta-Margin is Clinton +4.24%. This is nearly identical to today’s HuffPollster national-poll estimate, Clinton +4.3%. So state and national polls are perfectly matched at the moment. Note that national polls sample more frequently tend to capture swings in opinion before the state poll aggregate does. If Hillary Clinton’s current downswing lasts long enough, it will soon become apparent in the state-poll snapshot.

Obviously, enough states are safely Democratic or Republican that the number of possible outcomes is far less than 2.3 quadrillion. Only about 14 states are in play, for 16,384 possibilities. I use polls for all 50 states and the District of Columbia where available. In races lacking polls, usually in places where the outcome is not much in doubt, I use the result from the 2012 Obama-Romney race as a starting assumption. There has been a lot of talk this year about how all bets are off. However, as I showed a few weeks ago, Donald Trump has not scrambled the electoral map in any meaningful way. The sole exception so far is Utah, where Trump is running over 30 percentage points weaker against Clinton than Barack Obama did against Mitt Romney. However, Utah is so strongly Republican that this is probably not going to change the November outcome.

On the off chance that sparsely-polled states start to look competitive, or if evidence emerges that the electoral map is actually scrambled, I am considering using the Google Correlate method to fill in missing data. Google Correlate was remarkably useful tool in the primaries, and is an attractive alternative to using 2012 election results.

Estimating the probability of a November outcome requires an estimate of how far polls may move in the coming 160 days or so. I calculate a November win probability based on the simple assumption that polls are likely to move as much as they have in past races from 1952-2012. The idea is that state polls are accurate in the home stretch, but may move (all states together) by an amount that can be estimated using the movement in national opinion. Past movement since 1952 serves as a guide to the likely range of movement.

I mentioned before that February/March/April polls may be slightly more predictive than May/June polls. One possible reason is what Charlie Cook pointed out today is the case this year: the Democratic Party’s nomination process is not settled. He suggests that Clinton’s dip in polls is likely to be temporary, and that she should bounce back after the last primaries on June 7th. Logically, that might suggest using a longer time window of polls for making a November prediction. For now my inclination is to just use the current snapshot as a starting point, which has the disadvantage of giving a prediction that may move around too much…but has the advantage of being transparently based on today’s snapshot, which I think is more in keeping with the spirit of this website.

Note that 2000-2012 showed less variation than 1952-1996. By using a historical baseline period spanning more elections, I am making a conservative assumption that allows for the possibility of a large change, as occurred in 1964 (Johnson v. Goldwater) or 1980 (Carter v. Reagan). For a further discussion of what baseline period is appropriate to use, see this PEC thread.

Let me close with a broad statement. In the news you will see some rather hysterical statements about how all bets are off this year. That is true to an extent: on the Republican side, the national party’s positions and their rank-and-file voters’ preferences are far out of whack. In a deep sense, their decision process in 2016 became broken. But that does not mean that opinion is unmeasurable. Far from it. In the aggregate, pollsters still do a good job reaching voters. And voters are still people whose opinions move at a certain speed. To my thinking, polls may be the best remaining way to assess what is happening.