@article {heckman2012, title = {The theory and application of penalized methods or Reproducing Kernel Hilbert Spaces made easy}, journal = {Statist. Surv.}, volume = {6}, year = {2012}, pages = {113{\textendash}141}, publisher = {The American Statistical Association, the Bernoulli Society, the Institute of Mathematical Statistics, and the Statistical Society of Canada}, doi = {10.1214/12-SS101}, url = {http://dx.doi.org/10.1214/12-SS101}, author = {Heckman, Nancy} }