Model assumption for constant and changing FOI

[yungwai-chan]

It is probably a question more than an issue. I have fitted all 3 models with my data for an endemic infection (chickenpox) without intervention (immunisation programme). The fast time-varying foi model fits better than the slow time-varying foi, with the constant foi model having the lowest ELDP.

Some endemic infection like chickenpox does have cyclical pattern every few years, and certain cohorts may experience higher FOI than the others. But I wonder if the fast time-varying FOI fits best may come from the uncertainty in sampling as well? Often the youngest age group will have the largest sample size and sometimes the older age groups may have varying seroprevalence (not uniformly high), potentially due to sampling issue or smaller sample size. In that case perhaps the time-varying model fit the 'imperfect' data better?

Also it will be great to have option to visualise the prior distribution, especially if this could be customised later.