Minimum cost effective difference (MCED) serves as the smallest improvement in an outcome instrument that is associated with a cost-effective response to surgery. With the use of cost-effective anchor of < $50 000/quality-adjusted life year (QALY), MCED after transforaminal lumbar interbody fusion was 4 points for visual analog scale for low back pain, 3 points for visual analog scale for leg pain, 22 points for Oswestry Disability Index, and 0.31 QALYs for EuroQol 5D ¹⁾