Data Envelopment Analysis (DEA) was employed as a performance evaluation method for bank branches to assess their relative efficiency, and the reference set concept provided by the DEA results was used to demonstrate consistency with the opinions of managers regarding selected exemplary branch groups. Using various ratios actually employed in performance evaluation by the bank selected for this study, a simulated index was calculated, and the relative evaluation results based on this simulated index were compared and analyzed against the DEA efficiency results. By dividing the evaluated branches into two groups using two scale variables and comparing the DEA efficiency means of the two groups through a t-test, it was demonstrated that economies of scale exist. This approach differs from the traditional method of verifying economies of scale based on coefficient analysis of cost function regression equations.