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Table 1 Baseline characteristics of the two groups and imbalance between the original (unweighted) and propensity score—weighted groups

From: Intrathecal morphine in combination with bupivacaine as pre-emptive analgesia in posterior lumbar fusion surgery: a retrospective cohort study

Characteristic Level Spinal anaesthesia (ITM + 0.25% bupivacaine) Propensity weighting
No Yes SMD (%; before) SMD (%; after)
n   40 26   
Gender (%) F 24 (60.0) 14 (53.8) 12.5 10.0
M 16 (40.0) 12 (46.2)   
Age (mean (SD)) 48.77 (12.82) 52.42 (13.17) 28.1 6.0
ASA grade (%) 1 19 (47.5) 14 (53.8) 12.7 7.7
2 19 (47.5) 10 (38.5) − 18.3 − 9.4
3 2 (5.0) 2 (7.7) 11.1 3.3
Levels (%) 1 17 (42.5) 11 (42.3) 10.7 8.1
2 22 (55.0) 12 (46.2)   
3 0 (0.0) 2 (7.7)   
4 0 (0.0) 1 (3.8)   
5 1 (2.5) 0 (0.0)   
  1. Propensity-score matching was based on all four baseline characteristics
  2. Standardised mean difference (SMD), expressed as %. The number of levels was considered a continuous variable in the propensity score analysis