Kenward, M. G., & Roger, J. H. (1997). Small Sample Inference for Fixed Effects
from Restricted Maximum Likelihood. Biometrics, 53, 983-997.
Kuznetsova, A., Brockhoff, P. B., & Christensen, R. H. B. (2017). lmerTest
Package: Tests in Linear Mixed Effects Models. Journal of Statistical Software,
82(13), 1-26. <doi: 10.18637/jss.v082.i13>.