Hello SAS Community, I'm doing 1:1 propensity score matching procedure The data set contains 47366 samples (treatment=30694/ control=16672) After PROC PSMATCH procedure, I got a table as below The number of All Obs (Treatment) and All Obs (Control) is different from the original data set, 70 of the total sample were lost.  And I also got a warning: Some treated units do not have matched controls because there are not enough available controls for these treated units. Is this problem related to the warning? How do I solve it? proc psmatch data=B.HLP_ID_COMED region=treated; class SEX statin c_htn c_dm c_os c_mg c_go c_as c_sch c_emd c_nd c_dp c_thy c_gl m_antihi m_bb m_diur m_ssri m_anticho m_ppi m_glau ; Psmodel statin (Treated='1')= AGE SEX c_htn c_dm c_os c_mg c_go c_as c_sch c_emd c_nd c_dp c_thy c_gl m_antihi m_bb m_diur m_ssri m_anticho m_ppi m_glau; match method=greedy( k=1) exact=(SEX) caliper=0.2 ; assess lps var=(AGE SEX c_htn c_dm c_os c_mg c_go c_as c_sch c_emd c_nd c_dp c_thy c_gl m_antihi m_bb m_diur m_ssri m_anticho m_ppi m_glau)/plots=ALL weight=none; output out(obs=match)=OUT_PSM matchid=_MatchID; run; ... View more