Measurement of the validity of utility elicitations performed by computerized interview.

OBJECTIVES

The authors evaluate a measure of the validity of utility elicitations and study the potential effects of invalid elicitations on population utility values.

METHODS

The authors used a computerized survey to describe and measure preferences for three common side-effects of anti-psychotic drugs (tardive dyskinesia [TD], akathesia [AKA], pseudo-parkinsonism). The authors compared the validity of elicitations in 41 healthy volunteers to 22 schizophrenic patients. Preferences were measured using visual analog scale (VAS), pair-wise comparison (PWC), and the Standard Gamble (SG) methods. To assess the validity of each groups' responses, the authors compared the consistency of subjects' rank-order of the desirability of states across methods of preferences assessment (CAMPA).

RESULTS

All healthy volunteers and 82% of patients completed the computer survey; of these subjects, 97% of healthy volunteers and 70% of patients indicated they thought they understood the task required of them. However, only 78% of healthy subjects and 44% of patients had a consistent rank ordering of preferences among VAS and PWC ratings; only 80% and 61%, respectively, had a consistent rank ordering preferences among SG and PWC ratings. For two of the three health states, inconsistent subjects had statistically higher SG utilities (for TD, 0.94 versus 0.87, and for AKA 0.92 versus 0.86; P < 0.05).

CONCLUSIONS

The CAMPA test can identify potentially invalid preference ratings. Potentially invalid preference ratings may bias the "population" utilities for health states.