Purpose: Indirect comparison (IC) and direct comparison (DC) of four inhaled corticosteroid (CS) treatments for asthma were conducted, and the factors that may influence the results of IC were investigated. Among those factors, we focused on the effect of common comparator selection in the treatment of asthma, where little control group bias or placebo effect is expected. Method: IC and DC were conducted using the change from baseline in forced expiratory volume in 1 s (FEV1(L)) as an outcome parameter. Differences between inhaled CS were evaluated to compare the results of IC and DC. As a common comparator for IC, placebo (PLB) or mometasone (MOM) was selected. Whether the results of IC are affected by the selection of a common comparator and whether the results of IC and DC are consistent were examined. Results: 23 articles were identified by a literature search. Our results showed that ICs yielded results similar to DCs in the change from baseline of FEV1(L). No statistically significant difference was observed in inconsistency analysis between ICs and DCs. It was clinically and statistically confirmed that ICs with PLB and those with MOM did not differ in terms of the results of FEV1(L) analysis in this dataset. Conclusion: This study demonstrated that ICs among inhaled CS can deliver results consistent with those of DCs when using the change from baseline in FEV1(L) as an outcome parameter in asthma patients. It was also shown that using an active comparator has similar results if there is no effect of control group bias. It should be emphasized that the investigation of control group bias is a key factor in conducting relevant ICs so that an appropriate common comparator can be selected.
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