We would like to thank Simon Chapple, Michael Fletcher, Vasantha Krishnan, Marlene Levine, Ron Lovell, Ross Mackay, Graeme Parker, Nick Pole, Ann Reeves, Rachel Smithies, Bob Stephens and two anonymous referees for their helpful comments on earlier drafts of this paper; Sathi Sathiyandra for his assistance with
SWIFTT data; Justine Auton, Mike O'Rourke and Sue Meehan for advice on administrative processes around inclusion of children in benefits; and Bill Boddington of Statistics New Zealand for advice on births registrations data.