Selection of items and avoidance of bias in quality of life scales.

The total score of a quality of life (QOL) questionnaire reflects the items that make up the questionnaire. Although different questionnaires have strikingly similar items, the balance between types of items can affect research outcomes. Four general quality of life (QOL) scales and one specific scale may be compared to show how the balance of items can bias the results to: (a) increase or decrease the chance of obtaining a significant result in a clinical trial; (b) make one treatment appear better or worse compared with that of a competitor; (c) make the QOL of one disease category appear better or worse than that of another disease category. Healthcare decision-making should be based on relatively unaggregated measures of health.