If you use MATCHIT, please cite
Daniel Ho; Kosuke Imai; Gary King; and Elizabeth Stuart (2007), ``Matching as Nonparametric Preprocessing for Reducing Model Dependence in Parametric Causal Inference,'' Political Analysis 15(3): 199-236, http://gking.harvard.edu/files/abs/matchp-abs.shtml.
and
Daniel Ho; Kosuke Imai; Gary King; and Elizabeth Stuart (2007b) ``Matchit: Nonparametric Preprocessing for Parametric Causal Inference,'' Journal of Statistical Software, http://gking.harvard.edu/matchit/.
In addition, the convex.hull discard option is implemented via the WhatIf package (, ,,). Generalized linear distance measures are implemented via the stats package (, ). Generalized additive distance measures are implemented via the mcgv package (, ). The neural network distance measure is implemented via the nnet package (, ). The classification trees distance measure is implemented via the rpart package (, ). Full and optimal matching are implemented via the optmatch package (, ). Genetic matching is implemented via the Matching package (, ). Coarsened exact matching is implemented via the cem package (, ,).