

   CCaallccuullaattee TThhiirrdd OOrrddeerr CCuummuullaannttss

        cum3(a, b=a, c=a, unbiased=T)

   AArrgguummeennttss::

          a: A vector of observations.

          b: Another vector of observations,  if not supplied
             it is set to the value of `a'.  If supplied then
             it must be the same length as `a'.

          c: Another vector of observations,  if not supplied
             it is set to the value of `a'.  If supplied then
             it must be the same length as `a'.

   unbiased: A logical value indicating whether the unbiased
             estimator should be used.

   DDeessccrriippttiioonn::

        Calculates an estimate of the third cumulant, or skew-
        ness, of a vector.  Also, if more than one vector is
        specified, a product-moment of order 3 is estimated.

   DDeettaaiillss::

        The unbiased estimator uses a multiplier of
        `n/((n-1)*(n-2))' where `n' is the sample size, if
        `unbiased' is `FALSE' then a multiplier of `1/n' is
        used.  This is multiplied by `sum((a-mean(a))*(b-
        mean(b))*(c-mean(c)))' to give the required estimate.

   VVaalluuee::

        The required estimate.

