15.17. A baseline-category logit model fit predicting preference for U.S. President (Democrat, Republican, Independent) using x = annual income (in $10,000) is log(D/ I) =

15.17. A baseline-category logit model fit predicting preference for U.S. President (Democrat, Republican, Independent)

using x = annual income (in $10,000) is log(πˆD/πˆ I) = 3.3 − 0.2x and log(πˆR/πˆ I) = 1.0 + 0.3x.

(a) For each equation, interpret the sign of the estimated effect of x.

(b) Find and interpret the prediction equation for log(πˆR/πˆD).

(c) Use an estimated odds ratio to describe how the choice between Republican and Democrat depends on income.