Table 1.

HGAM model descriptions, corresponding to the $f_j$ functions in equation (2.1). All models contain the common intercept term, the same log-link function and a negative-binomial distribution for the response variable.

model	description
G	single smooth function of latitude, longitude and week, fixed across variants
I	fixed factor slope for each variant; smooth function of latitude, longitude and week, estimated separately for each variant and with different levels of smoothness
S	smooth function of latitude, longitude and week, estimated separately for each variant, but assumed to have same level of smoothness
GI	as model I, but with additional smooth function of latitude, longitude and week shared across all variants
GS	as model S, but with additional smooth function of latitude, longitude and week shared across all variants