This method dispatches on the type of model$human.
observe_pfpr(model, parameters)an array of counts, with actual condition as first dimension and tested condition as the second dimension, and the third dimension is the human strata
an object from make_MicroMoB
a named list, should have elements sens (sensitivity),
spec (specificity), and a vector of length equal to number of strata testprop
which gives the proportion of each strata to be tested.