re arbitrary weights which can be used by the actuary to downweight any
outlying Fik. Normally, Wik = I for all i, k. Then, a = 1 gives the historical
chain ladder age-to-age factors, a = 0 gives the straight average of the
observed individual development factors and a = 2 is the result of an
ordinary regression of Ci,k+f against Cik with intercept 0. Note that in case
Ca-= 0, the corresponding two summands should be omitted when
calculating fk.
The above stepwise rule finally leads to the prediction