Past exam of the mathematics course of the University of Cambridge / 2024 / ii / Paper 4 / 13L / a / Solution

With $p_i=\mathbb{P}({\mathrm{dis}}_i=1)$, the fitted logistic model isRisk category 1 is the reference level, so its effect is included in the intercept; adding a separate coefficient for both levels would make the design matrix linearly dependent.