Pre-built psi_func_rcpp from
makeRobustbasePsi("lqq") with robustbase's default lqq
tuning (about 95% efficiency at the normal). The lqq psi of Koller and
Stahel (2011) redescends more gradually than the bisquare and is the
recommended redescender, as used by robustbase's
lmrob.control(setting = "KS2014"). Use it as
rho.e in rlmer; a redescender needs a good initial
estimate, so pair it with init = "ransac" or
rlmer_ransac.
Koller, M. and Stahel, W. A. (2011) Sharpening Wald-type inference in robust regression for small samples. Computational Statistics & Data Analysis 55(8), 2504--2515.
makeRobustbasePsi, bisquarePsi.