@article{Heisig2019,
author = {Heisig, J.P. and Schaeffer, M.},
title= {Why you should always include a random slope for the lower-level variable involved in a cross-level interaction},
year = {2019},
doi = {10.1093/esr/jcy053},
volume = {35},
number = {2},
pages = {258--279},
}