Error given is below:
Error in quantile.default(resid) : factors are not allowed
Inoltre: Warning messages:
1: In model.response(mf, "numeric") :
using type = "numeric" with a factor response will be ignored
2: In Ops.factor(y, z$residuals) : ‘-’ not meaningful for factors
3: In Ops.factor(r, 2) : ‘^’ not meaningful for factors