The effect of different methods of collecting data: mail, telephone and filter data collection issues in utility measurement.

When collecting data researchers can interview participants, conduct telephone interviews, or mailout questionnaires. Often mixed methods are used. Whether these methods produce equivalent data is under-researched in the health-related quality of life (HRQoL) field. In addition, the effect of using filter questions has not been researched among HRQoL multi-attribute utility instruments. This study randomly sampled from Melbourne, Australia, and employed a test-retest design to investigate whether mail or telephone interview made any difference to Assessment of Quality of Life (AQoL) instrument utility scores. A filter question AQoL version investigated the effect of filters on scores. There was no significant difference in standard AQoL scores between mail self-completion and telephone interview, regardless of which was administered first. Inclusion of filter questions encouraged respondents to select the best response category thereby screening out minor health conditions. The effect was to increase utility scores by 0.06 or 7%. This effect has not been previously reported in utility instruments and has profound implications for economic evaluations using cost-utility analysis; there are implications for researchers using filter questions in general. In conclusion, researchers should feel confident that utility scores elicited from the standard AQoL through self-completion mail and telephone interview administrations are directly comparable.