Observed curvature (-d^2 log-lik / d eta^2 at the realized y), elementwise.
Source: R/family_loglik.R
dot-family_obs_weight.RdFalls back to the y-free weight for families whose curvature carries no
y – those where the response enters the log-likelihood linearly in eta
(Poisson, binomial, and the zero-truncated Poisson), for which the observed
and expected curvature coincide identically rather than only in expectation.