求助各位大神,我做PSM时出现这种情况是怎么回事呢?
psmatch2 pa x1 x2 x3 x4 x5 x6 x7 x8 x9,outcome(pv) n(1)ate ties logit common
outcome does not vary; remember:
0 = negative outcome,
all other nonmissing values = positive outcome
希望大家多多指点


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