Model

Because I had three possible outcomes, and because there is no natural ordering among the outcomes, I ended up using a categorical model.

\[ vote_i \sim Categorical(\rho_{trump}, \rho_{biden}, \rho_{jorgensen}) \]

Here is the mathematical equation I used.

\[ \begin{aligned} \rho_{biden} &=& 1 - \rho_{trump} - \rho_{jorgensen}\\ \rho_{trump} &=& \frac{e^{-0.22 - 0.38 northeast + 0.15 south - 0.39 west}}{1 + e^{-0.22 - 0.38 northeast + 0.15 south - 0.39 west}}\\ \rho_{jorgensen} &=& \frac{e^{-3.4 - 0.49 northeast -0.24 south - 0.36 west}}{1 + e^{-3.4 - 0.49 northeast -0.24 south - 0.36 west}}\\ \end{aligned} \] Now we can look at our regression table, which shows our expected values.

Characteristic

Beta

95% CI

1
muJorgensen_(Intercept) -3.4 -3.8, -3.0
muTrump_(Intercept) -0.22 -0.32, -0.12
muJorgensen_regionNortheast -0.49 -1.1, 0.16
muJorgensen_regionSouth -0.24 -0.77, 0.30
muJorgensen_regionWest -0.36 -0.95, 0.21
muTrump_regionNortheast -0.38 -0.54, -0.22
muTrump_regionSouth 0.15 0.02, 0.28
muTrump_regionWest -0.39 -0.54, -0.24
1

CI = Credible Interval

If we want to calculate the posterior probability, we substitute these values into the equation above.