quokarR package for diagnosing quantile regression modelsquokar can be easily installed on Windows and Linux using command:devtools::install_github("wenjingwang/quokar")To install quokar on Mac, you need to install a fortran compiler.You can install gfortran by command,curl -O http://r.research.att.com/libs/gfortran-4.8.2-darwin13.tar.bz2 sudo tar fvxz gfortran-4.8.2-darwin13.tar.bz2 -C /