title: Determination of the minimum improvement in pain, disability, and health state associated with cost-effectiveness: introduction of the concept of minimum cost-effective difference.
abstract: BACKGROUND
  Minimum clinical important difference (MCID) has been adopted as the smallest improvement in patient-reported outcome needed to achieve a level of improvement thought to be meaningful to patients.
  
  
  OBJECTIVE
  To use a common MCID calculation method with a cost-utility threshold anchor to introduce the concept of minimum cost-effective difference (MCED).
  
  
  METHODS
  Forty-five patients undergoing transforaminal lumbar interbody fusion for degenerative spondylolisthesis were included. Outcome questionnaires were administered before and 2 years after surgery. Total cost per quality-adjusted life-year (QALY) gained was calculated for each patient. MCED was determined from receiver-operating characteristic curve analysis with a cost-effective anchor of < $50,000/QALY and < $75,000/QALY. MCID was determined with the health transition item as the anchor.
  
  
  RESULTS
  Significant improvement was observed 2 years after transforaminal lumbar interbody fusion for all outcome measures. Mean total cost per QALY gained at 2 years was $42,854. MCED was greater than MCID for each outcome measure, meaning that a greater improvement was required to represent cost-effectiveness than a clinically meaningful improvement to patients. The area under the receiver-operating characteristic curve was consistently ≥ 0.70 with both cost-effective anchors, suggesting that outcome change scores were accurate predictors of cost-effectiveness. Mean cost per QALY gained was significantly lower for patients achieving compared with those not achieving an MCED in visual analog scale for leg pain ($43,560 vs $112,087), visual analog scale for back pain ($41,280 vs $129440), Oswestry Disability Index ($30,954 vs $121,750), and EuroQol 5D ($35800 vs $189412).
  
  
  CONCLUSIONS
  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/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.
authors.affiliation: Department of Neurosurgery, Vanderbilt University Medical Center, and Vanderbilt Spinal Column Surgical Quality and Outcomes Research Laboratory, Nashville, Tennessee.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Parker
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McGirt
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003362:Cost-Benefit Analysis; D005260:Female; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000150:complications / Q000601:surgery*; D017116:Low Back Pain / Q000209:etiology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D063868:Patient Outcome Assessment; D019057:Quality-Adjusted Life Years; D012680:Sensitivity and Specificity; D013123:Spinal Fusion / Q000191:economics*; D013168:Spondylolisthesis / Q000150:complications / Q000601:surgery*