In reality, what is fixed and what is not is itself a policy choice. If immigration
generates a fiscal gain then the question of how that is divided up is an object of
political debate not an input into it. As Scholten and Thum (1996) point out, pivotal
political agents – in typical models, the median voter – will not usually be modelled as
taking account of the effects of immigration on others and chosen immigration policy
can be correspondingly inefficient