Is a single-item visual analogue scale as valid, reliable and responsive as multi-item scales in measuring quality of life?

Abstract

Purpose: To compare the validity, reliability and responsiveness of a single, global quality of life question to multi-item scales. Method: Data were obtained from 83 consecutive patients with oesophageal adenocarcinoma undergoing either transhiatal or transthoracic oesophagectomy. Quality of life was measured at baseline, 5 weeks, 3 and 12 months post-operatively with a single-item Visual Analogue Scale (VAS) ranging from 0 to 100, the multi-item Medical Outcomes Study Short Form-20 (MOS SF-20) and Rotterdam Symptom Check-List (RSCL). Convergent and discriminant validity, test-retest reliability and both distribution-based and anchor-based responsiveness were evaluated. Major findings: At baseline and at 5 weeks, the VAS showed high correlations with the MOS SF-20 health perceptions scale (r = 0.70 and 0.72) and moderate to high correlations with all other subscales of the MOS SF-20 and RSCL (r = 0.29-0.70). The test-retest reliability intra-class correlation for the VAS was 0.87. At 5 weeks post-operatively, the distribution-based responsiveness was moderate for the VAS (standardised response mean: -0.47; effect size: -0.56), high for the physical subscales of the MOS SF-20 and RSCL (-1.08 to -1.51) and low for the psychological subscales (0.11 to -0.25). Five weeks post-operatively, anchor-based responsiveness was highest for the VAS (r = 0.54). Conclusion: The VAS is an instrument with good validity, excellent reliability, moderate distribution-based responsiveness and good anchor-based responsiveness compared to multi-item questionnaires. Its use is recommended in clinical trials to assess global quality of life.