1step,rule,n_before,n_after,n_removed,rationale21,drop quarters before 1960Q1,319,267,52,outside question window (1959Q4 levels used only for differencing)32,drop quarters after 2019Q4,267,240,27,information rule: post-2019Q4 must not enter any estimate43,drop quarters with missing du or g,240,240,0,incomplete data5