@inbook{Sikkel2009,
author = {Sikkel, D. and Hox, J. and de Leeuw, E. },
title= {Using auxiliary data for adjustment in longitudinal research},
year = {2009},
doi = {10.1002/9780470743874.ch9},
editor = {Peter Lynn, P.},
booktitle = {Methodology of longitudinal surveys},
address = {Chichester, UK},
publisher = {Wiley},
pages = {141−156},
}