Sum to zero for BYM2 unstructured effect

Modeling
3

Thanks @mitzimorris – my understanding is that \theta \times \sigma is basically a random effect specified via non-centred parametrisation, and as such it’s “soft” centred (correct me if I’m wrong). Based on my reading of this thread, I had understood that it was preferable for posterior-sampling efficiency gains to specify traditional random intercepts with the sum_to_zero formulation where possible. Did I get that wrong ? Thanks again.