“…The problem of re-estimating linear models after adding (updating) or removing (downdating) observations has already been addressed [6,11,13,14,16,17,26,29,33]. Methods had previously been proposed for the effective estimation of the SEM [1,6,8,18,20], however, the sequential derivation of the 3SLS estimator for large-scale SEMs has not, previously, been considered.…”