I think you wrote 'demographer' when thinking 'economist'.
Partly i was thinking of another post i was typing at the same time but a demographer would be far better at determining where in our society immigrants had moved and how productive they may or may not be though your economist would be better suited to putting a $ value on it. For example a demographer would be better suited to tell you what % of a certain migrant group became convicted criminals whereas the economist could tell you what it cost to keep them in prison.
Both would be invaluable in any serious analysis of Immigration and its net cost /benefit.
Mutation