What is the difference between Hierarchical GAMs (HGAM) and Mixed GAMs (GAMM), if any?
I am looking to model time series of count data against a range of candidate explanatory variables (hoping to understand which environmental parameters could explain the fluctuations). I have a year of data at 7 sites, quite different from each other in terms of environment, but not completely independent (species can easily move from one to another).
I struggle to identify which of the two frameworks would be the most appropriate. A HGAM with grouping per site, or a GAMM with site as a random variable... Is there any key difference I am missing here?
Thank you for any advice!