1step,rule,n_before,n_after,n_removed,rationale21,drop rows with missing school_id/treated/score,1000,1000,0,cannot be used in OLS32,drop exact duplicate rows,1000,1000,0,duplicate records43,drop duplicated student_id (keep first),1000,1000,0,student_id must be unique54,treated must be 0/1,1000,1000,0,binary treatment65,drop schools with non-constant treated,1000,1000,0,treatment must be constant within school7