Estimation of minimally important differences in EQ-5D utility and VAS scores in cancer.
BACKGROUND
Understanding what constitutes an important difference on a HRQL measure is critical to its interpretation. The aim of this study was to provide a range of estimates of minimally important differences (MIDs) in EQ-5D scores in cancer and to determine if estimates are comparable in lung cancer.


METHODS
A retrospective analysis was conducted on cross-sectional data collected from 534 cancer patients, 50 of whom were lung cancer patients. A range of minimally important differences (MIDs) in EQ-5D index-based utility (UK and US) scores and VAS scores were estimated using both anchor-based and distribution-based (1/2 standard deviation and standard error of the measure) approaches. Groups were anchored using Eastern Cooperative Oncology Group performance status (PS) ratings and FACT-G total score-based quintiles.


RESULTS
For UK-utility scores, MID estimates based on PS ranged from 0.10 to 0.12 both for all cancers and for lung cancer subgroup. Using FACT-G quintiles, MIDs were 0.09 to 0.10 for all cancers, and 0.07 to 0.08 for lung cancer. For US-utility scores, MIDs ranged from 0.07 to 0.09 grouped by PS for all cancers and for lung cancer; when based on FACT-G quintiles, MIDs were 0.06 to 0.07 in all cancers and 0.05 to 0.06 in lung cancer. MIDs for VAS scores were similar for lung and all cancers, ranging from 8 to 12 (PS) and 7 to 10 (FACT-G quintiles).


CONCLUSIONS
Important differences in EQ-5D utility and VAS scores were similar for all cancers and lung cancer, with the lower end of the range of estimates closer to the MID, i.e. 0.08 for UK-index scores, 0.06 for US-index scores, and 7 [corrected] for VAS scores.
D000203:Activities of Daily Living; D002173:Cancer Care Facilities; D003430:Cross-Sectional Studies; D018450:Disease Progression; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology*; D008297:Male; D009367:Neoplasm Staging; D009369:Neoplasms / Q000188:drug therapy / Q000503:physiopathology* / Q000523:psychology*; D011594:Psychometrics; D011788:Quality of Life; D012189:Retrospective Studies; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D006113:United Kingdom; D014481:United States; D026712:Value of Life