hether to use the
  <code>calibrate</code> or <code>postStratify</code> function is dictated by the format
  of popsize, which is discussed below.  Post-stratification adjusts the
  sampling and replicate weights so that the joint distribution of a set of
  post-stratifying variables matches the known population joint distribution.
  Calibration, generalized raking, or GREG estimators generalize
  post-stratification and raking by calibrating a sample to the marginal
  totals of variables in a linear regres