For any equal
in the ordered set, say
, a single observation
is returned with a corresponding
and
, calculated as:
and
Observations with zero weight are ignored. If no weights are supplied by you, then unit weights are assumed; that is
, for
.
In addition, the within group sum of squares is computed for the tied observations using West's algorithm (see
West (1979)).
For a discussion on the accuracy of the algorithm for computing mean and variance see
West (1979).
nag_order_data (g10zac) may be used to compute the pure error sum of squares in simple linear regression along with
nag_regsn_mult_linear (g02dac), see
Draper and Smith (1985).