Depression-free day to utility-weighted score: is it valid?

Area of Science:

• Health Economics
• Psychiatry
• Quality of Life Research

Background:

• Cost-utility analyses increasingly use formulas to convert depression-free days (DFDs) into utility scores.
• These formulas rely on linear extrapolation of the relationship between depression severity and health-related quality of life.

Purpose of the Study:

• To validate existing formulas that convert DFDs to utility weights for depression interventions.
• To assess the accuracy of these DFD-based utility weights compared to direct quality-of-life measures.

Main Methods:

• An observational study tracked 77 major depression patients over 12 months.
• Depression severity was measured using HAM-17 and BDI; quality of life used QWB-SA.
• DFDs were calculated and converted to utility weights to estimate quality-adjusted life years (QALYs).

Main Results:

• QALYs estimated directly from QWB-SA were lower than those from utility-weighted DFD calculations.
• Incremental QALYs did not differ significantly between methods.
• Adjusting the BDI conversion factor or severity range improved its fit with QWB-SA.

Conclusions:

• The existing HAM-17 utility-weighted formula is supported for cost-utility analyses.
• Modifications to the BDI formula are suggested for improved accuracy.
• These DFD-based formulas offer reasonable alternatives when direct quality-of-life measures are unavailable.