Coaching Variables for Regression and Classification
  Robert Tibshirani
  Department of Public Health Sciences and Department of Statistics
  University of Toronto
  Geoffrey E. Hinton 
  Department of Computer Science
  University of Toronto
  Abstract
  In a regression or classification setting where we wish to predict Y
  from x1,x2,
, xp, we suppose that an additional set of coaching variables
  z1,z2,
, zm are available in our training sample. These might be variables that are
  difficult to measure, and they will not be available when we predict Y from x1,x2,
,
  xp in the future. We consider two methods of making use of the coaching variables in order
  to improve the prediction of Y from x1,x2,
, xp. The relative merits of these
  approaches are discussed and compared in a
  number of examples.
  Download:  [ps] [pdf]
  Statistics and Computing, 8, 25-33
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