2.5. Statistical analysis
The odds ratios (ORs) with 95% confidence intervals (CIs) for
dichotomous outcomes and standardized mean differences (SMDs) or mean
differences (MDs) with 95% CIs for continuous outcomes were calculated.
This network meta-analysis was
performed within a frequentist framework using the STATA 16.0
(StataCorp, Texas, USA) command ‘mvmeta’[20].
Firstly, the network geometry plot for each outcome was established,
which provided a visual and concise description between pairs of
interventions[21]. Secondly, statistical
consistency was evaluated by the node-splitting method and loop
inconsistency model. P-value ≥ 0.05 or the 95% CI for each closed-loop
contained 0 means direct comparison and indirect comparison were
considered consistent[22]. Thirdly, a
comparison-adjusted funnel plot was used to evaluate publication bias. A
symmetrical graph indicated a low influence of publication bias and an
asymmetric graph meant possible publication bias. Finally, the forest
plot was constructed to report the results for the mixed comparison
between interventions and placebo, and the league table was performed to
illustrate all head-to-head comparisons. We assumed that 95% CIs not
containing 0 were considered statistically significant for SMDs or MDs,
and those not containing 1 were considered statistically significant for
ORs. The two-dimensional graph is presented to visualize the
comprehensive comparisons of drugs to placebo. The point which lies to
the lower-left portion of the coordinate system and does not intersect
with the dark grey dashed line indicates that this pharmacological
intervention is superior to placebo in terms of both postoperative pain
intensity and the incidence of PONV. Additionally, the ranking
probabilities were estimated for all interventions of being at each
possible rank of each intervention[21]. By using
the ranking probabilities, the treatment hierarchy was summarized and
reported as the surface under the cumulative ranking curve
(SUCRA)[21]. The larger the SUCRA value is, the
better are the rank of the treatment for outcomes.