Hi everyone,

I am trying to determine the change in the posterior distributions of `marginals.fitted.values` between two Stochastic Partial Differential Equation (SPDE) models, akin to the methodologies employed in this guide: https://www.paulamoraga.com/bo…aldataexamplespatial.html

The two models have been constructed utilizing the same spatial points, albeit with data from two distinct years. My aim is to discern whether there has been a shift in the disease's prevalence over these two different timeframes. As a result, I've chosen to compute the difference between the posterior distributions of the `marginals.fitted.values` from both models.

I initially believed this could be achieved with a straightforward subtraction, however, the complexity of the `marginals.fitted.values` structure has proven this to be unfeasible.

I tried this but it I did not have any success:

Thank you in advance.