Title: Model assumptions
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The model used to track polling in the 2024 presidential election has changed. It was developed in March 2024 when President Biden and former President Trump were the presumptive nominees. The 2020 election was selected for two reasons:
- The same candidates
- The same swing states in play
The models showed an erosion of Biden's 2020 winning margins consistent with his lagging performance in polling.
The models for July after Biden's withdrawal and in August before and after the Democratic convention showed Harris first stabilizing the erosion from the 2020 results, but the most recent model showed no change at all, despite much improved polling numbers. As a result, the appropriateness of the 2020 election as a starting point fell into question and it was concluded that too great a weight was being given to it and a new initial set of values was needed to better reflect the current situation.
A broad political consensus still exists that the 2024 election will be very close in the seven swing states that will probably decide the election. The possibilities of breakout by one or the other party are also being discussed, but those are not yet manifest in polling.
Accordingly, the range of outcomes in the two-candidate margins was set at 0.48-0.52.
Because the election is drawing close, it is expected that polling will become increasingly reflective of the election. For one reason, some people polled may already have cast early ballots. Therefore, an adjustment was made that will allow the initial model to be modified by new polling to a greater degree.
<img src="/assets/img/models/PA_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/GA_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/NC_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/MI_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/AZ_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/WI_new_prior.png" style="width: 100%; display: block;">
<img src="/assets/img/models/NV_new_prior.png" style="width: 100%; display: block;">