Objective: To determine parent-child agreement for the Quality of My Life (QoML) questionnaire. To establish construct validity of the QoML questionnaire. To determine the minimal clinically important difference (MCID) for the Quality of Life (QOL) and Health-Related Quality of Life (HRQOL) scales.
Methods: A total of 136 families of children with inflammatory arthritis were interviewed. The QoML questionnaire was completed for the child's current state of health, and under 2 hypothetical scenarios, where (1) there is a hypothetical small improvement, and (2) there is a hypothetical small deterioration in health. The differences between the original QOL and HRQOL scores and hypothetical improvement and deterioration scores, respectively, were calculated to give MCID scores.
Results: In total, 131 families completed the questionnaires. Intraclass correlation coefficients for parent proxy report and patient self-report of the QOL and HRQOL were 0.63 and 0.40, respectively. Correlations of QOL with pain and disease severity were moderately negative (r = -0.55 and -0.56, respectively, p < 0.0001). Correlations of HRQOL with pain and disease severity were strongly negative (r = -0.66 and r = -0.68, respectively, p < 0.0001). The MCID for improvement on the QOL was 7 mm, and for the HRQOL 11 mm. The MCID for deterioration in QOL was -33 mm, and for HRQOL -38 mm.
Conclusion: The QoML questionnaire demonstrated fair parent-child agreement and good convergent construct validity. MCID scores will enable clinicians to interpret QoML questionnaire results in a clinically meaningful way.