1step,rule,n_before,n_after,n_removed,rationale20,drop quarters lacking GDPC1 or a complete 3-month UNRATE average,319,314,5,1947Q1-Q4 precede UNRATE start; 2025Q4 lacks Oct-2025 UNRATE; all outside window31,keep quarters 1959Q4-2019Q4 (levels),314,241,73,task window; 1959Q4 kept only for differencing42,drop 1959Q4 (no prior level for differences),241,240,1,first-difference loses one observation5