Validation of a short form Wisconsin Upper Respiratory Symptom Survey (WURSS-21)

Abstract

Background: The Wisconsin Upper Respiratory Symptom Survey (WURSS) is an illness-specific health-related quality-of-life questionnaire outcomes instrument.

Objectives: Research questions were: 1) How well does the WURSS-21 assess the symptoms and functional impairments associated with common cold? 2) How well can this instrument measure change over time (responsiveness)? 3) What is the minimal important difference (MID) that can be detected by the WURSS-21? 4) What are the descriptive statistics for area under the time severity curve (AUC)? 5) What sample sizes would trials require to detect MID or AUC criteria? 6) What does factor analysis tell us about the underlying dimensional structure of the common cold? 7) How reliable are items, domains, and summary scores represented in WURSS? 8) For each of these considerations, how well does the WURSS-21 compare to the WURSS-44, Jackson, and SF-8?

Study design and setting: People with Jackson-defined colds were recruited from the community in and around Madison, Wisconsin. Participants were enrolled within 48 hours of first cold symptom and monitored for up to 14 days of illness. Half the sample filled out the WURSS-21 in the morning and the WURSS-44 in the evening, with the other half reversing the daily order. External comparators were the SF-8, a 24-hour recall general health measure yielding separate physical and mental health scores, and the eight-item Jackson cold index, which assesses symptoms, but not functional impairment or quality of life.

Results: In all, 230 participants were monitored for 2,457 person-days. Participants were aged 14 to 83 years (mean 34.1, SD 13.6), majority female (66.5%), mostly white (86.0%), and represented substantive education and income diversity. WURSS-21 items demonstrated similar performance when embedded within the WURSS-44 or in the stand-alone WURSS-21. Minimal important difference (MID) and Guyatt's responsiveness index were 10.3, 0.71 for the WURSS-21 and 18.5, 0.75 for the WURSS-44. Factorial analysis suggested an eight dimension structure for the WURSS-44 and a three dimension structure for the WURSS-21, with composite reliability coefficients ranging from 0.87 to 0.97, and Cronbach's alpha ranging from 0.76 to 0.96. Both WURSS versions correlated significantly with the Jackson scale (W-21 R=0.85; W-44 R=0.88), with the SF-8 physical health (W-21 R=-0.79; W-44 R=-0.80) and SF-8 mental health (W-21 R=-0.55; W-44 R=-0.60).

Conclusion: The WURSS-44 and WURSS-21 perform well as illness-specific quality-of-life evaluative outcome instruments. Construct validity is supported by the data presented here. While the WURSS-44 covers more symptoms, the WURSS-21 exhibits similar performance in terms of reliability, responsiveness, importance-to-patients, and convergence with other measures.

Figure 1

Data shown represent Day 2 to Day 12. Sample size diminishes as participants’ colds resolve, from N=228 on Day 2 to N=100 on Day 12. The center of the notched boxes is the median summed score for that day. The notches portray the median ± 1.57 (interquartile range=IQR) / N^-2 and thus can be compared to assess difference at the P = 0.05 level of significance. The top of the notched boxes indicate the 25% and 75% percentiles, respectively. The ends of the vertical lines indicate the last actual data point within 1.5 (IQR) from the 25%ile and 75%ile. The symbols above and below these lines are actual outlying data points.

Figure 2

Data shown represent Days 2, 3 and 4, where sample size was N = 228, N = 226 and N = 224, respectively. Day 3 Pearson correlations (95% confidence intervals) against the WURSS-21 were 0.925 (0.903, 0.942) for the WURSS-44, 0.849 (0.808, 0.882) for Jackson, -0.793 (-0.739, -0.837) for SF-8 physical, and -0.547 (-0.448, -0.632) for SF-8 mental. Correlations to the WURSS-44 were 0.879 (0.846, 0.906) for Jackson, -0.799 (-0.746, -0.842) for SF-8 physical, and -0.599 (-0.507, -0.677) for SF-8 mental. Jackson correlated to SF-8 physical at -0.748 (-0.684, -0.800) and to SF-8 mental at -0.555 (-0.457, -0.640). All associations were statistically significant at p < 0.001.