

   WWeeiigghhtteedd AArriitthhmmeettiicc MMeeaann

        weighted.mean(x, w, na.rm=FALSE)

   AArrgguummeennttss::

          x: a numeric vector containing the values whose mean
             is to be computed.

          w: a vector of weights the same length as `x' giving
             the weights to use for each element of `x'.

      na.rm: a logical value indicating whether `NA' values in
             `x' should be stripped before the computation pro-
             ceeds.

   DDeessccrriippttiioonn::

        If `w' is missing then all elements of `x' are given
        the same weight.

        Missing values in `w' are not handled.

   SSeeee AAllssoo::

        `mean'

   EExxaammpplleess::

        ## GPA from Siegel 1994
        wt<- c(5/15,5/15,4/15,1/15)
        x <- c(3.7,3.3,3.5,2.8)
        xm <- weighted.mean(x,wt)

