A comparison of brief versus explicit descriptors for verbal rating scales: interrupted time series design.

BACKGROUND

Verbal rating scales (VRS) are widely used in patient-reported outcome (PRO) measures. At our institution, patients complete an online instrument using VRSs with a five-point brief response scale to assess symptoms as part of routine follow-up after ambulatory cancer surgery. We received feedback from patients that the brief VRS descriptors such as "mild" or "somewhat" were vague. We added explicit descriptors to our VRSs, for instance, "Mild: I can generally ignore my pain" for pain severity or "Somewhat: I can do some things okay, but most of my daily activities are harder because of fatigue" for fatigue interference. We then compared responses before and after this change was made.

METHODS

The symptoms investigated were pain, fatigue and nausea. Our hypothesis was that the explicit descriptors would reduce overall variance. We therefore compared the coefficient of variation of scores and tested the association between symptoms scores and known predictors thereof. We also compared time to completion between questionnaires with and without the additional descriptors.

RESULTS

A total of 17,500 patients undergoing 21,497 operations were assigned questionnaires in the period before the descriptors were added; allowing for a short transition period, 1,417 patients having 1436 operations were assigned questionnaires with the additional descriptors. Symptom scores were about 10% lower with the additional descriptors but the coefficient of variation was slightly higher. Moreover, the only statistically significant difference between groups for association with a known predictor favored the item without the additional language for nausea severity (p = 0.004). Total completion time was longer when the instrument included the additional descriptors, particularly the first and second time that the questionnaire was completed.

CONCLUSIONS

Adding descriptors to a VRS of post-operative symptoms did not improve scale properties in patients undergoing ambulatory cancer surgery. We have removed the additional descriptors from our tool. We recommend further comparative psychometric research using data from PROs collected as part of routine clinical care.