R package VariableScreening. Implements a screening procedure proposed by Chu, Li, and Reimherr (2016) for varying coefficient longitudinal models with ultra- high dimensional predictors <http://imstat.org/aoas/next_issue.html>. The effect of each predictor is allowed to vary over time, approximated by a low-dimensional B-spline. Within-subject correlation is handled using a generalized estimation equation approach with structure specified by the user. Variance is allowed to change over time, also approximated by a B-spline.