The electron effective mass (me) of Ga-doped ZnO (GZO) thin films is determined using electrical and spectroscopic ellipsometry measurements. The effects of different me used in the literature on electrical transport behavior and optical band gap shift are comparatively investigated to analyze the error qualitatively. The self-contradictory results of electrical transport behavior and the small deviation of optical band gap shift from the fixed me indicate that the accurate me has a more significant influence on the analysis of electrical transport behavior than the optical band gap shift. These results can be extended to other materials and provide a guideline to make the relevant analysis more accurate.