The first participant was enrolled on August 11, 2003. The last exited on August 21, 2007. This study was done in parallel with a randomized controlled trial testing echinacea, placebo effects, and doctor patient interaction in common cold[57
]. Joint recruitment methods targeted community members with new onset common cold. Of 2,169 responding callers, 534 were enrolled in that trial, and 239 were consented and enrolled in the validation study reported here. Of those enrolled, 230 were monitored through the duration of their colds, for a total of 2,457 person-days covered by this study.
Reasons for exclusion included symptom duration greater than 48 hours (462), allergy or asthma symptoms (50), failure to meet Jackson cold criteria (44), intended use of symptom-modifying medications (33), and subject judged to be unreliable (24). Reasons for non-enrollment of eligible callers included: participant burden (74), failure to return phone calls (65), failure to show up for enrollment (21), "not interested" (17), transportation problems (14), and insufficient compensation (5). Of the nine lost to follow-up, three people never returned phone calls, three reported losing their folders and never came in for their exit, two called to withdraw and never came in for their exit interview, and one person staying at a homeless shelter could not be contacted. Table portrays enrollment, monitoring and sociodemographic characteristics for the population sampled.
Time from first symptom to enrollment averaged 33.1 hours (SD = 13.4), inter-quartile range (25 to 45). Adding pre-enrollment illness hours to duration monitored (mean = 193.8, SD = 86.9) yields our estimate of mean total illness duration 226.9 hours (SD = 87.5), or 9.45 days. This may be an underestimate of actual average illness duration, as 40 (17.4%) participants continued to assess themselves as at least very mildly sick at the end of the maximum 14 day monitoring period.
Colds tend to begin with specific nasal or throat symptoms, or with nonspecific or general feelings of tiredness or malaise, sometimes difficult to quantify in terms of onset timing. In this sample, 97 (42%) people reported a sore or scratchy throat as their first symptom, with 105 (46%) reporting nasal discharge, obstruction or sneezing, and only 7 (3%) reporting cough as their first symptom. At enrollment, less than 48 hours from first symptom, 223 (97%) reported at least one nasal symptom, 201 (87%) had sore throat, and some 150 (65%) reported cough. Nonspecific symptoms were also highly prevalent, with 142 (62%) reporting headache, 87 (38%) chilliness, and 184 (80%) malaise, tiredness or lack of energy.
Severity of illness at enrollment varied greatly across all measures: WURSS-44, Jackson, and SF-8. Means, (standard deviations), and [interquartile ranges] were as follows: 9.54, (3.68), [7,12] for Jackson, 100.6, (51.2), [59, 134] for the WURSS-44, 40.3 (9.42) [33.3, 47.7] for SF-8 physical health, and 47.1 (9.34) [42.4, 54.4] for SF-8 mental health. Corresponding values for the WURSS global-severity-today item at enrollment were 4.10, (1.26), [3,5] Summary scores for the WURSS-44 and WURSS-21 are simple sums of all responses except the introductory global-severity-today score and the concluding global-change-since-yesterday items. This deviates from first reporting of WURSS validity,[24
] where global-severity-today was included in the summary score. We have since decided that "How sick do you feel today?" and "Please rate the average severity of your cold symptoms over the last 24 hours" refer to conceptually distinct time frames and hence should be not be lumped together in summary scores.
The pattern of experienced symptoms was characterized by the expected high frequency reporting of nasal symptoms (99.6%), sore or scratchy throat (97.8%), and cough (93.5%), reported at least once during the first seven days of illness. Sinus symptoms were also widely reported (92.2%), as were headache (89.6%) and body aches (88.7%). Other frequently reported symptoms were referable to the chest (73.9%), ears (77.0%), and eyes (83.5%). Swollen glands (67.4%), chilliness (63.9%) and feverishness (73.0%) were also experienced frequently. All N = 230 (100%) of our participants scored themselves as having some degree of tiredness, malaise, or feeling run down at least once during up to 7 days of illness. Some degree of functional limitation was also reported by 100% of our sample, with the following abilities receiving impairment scores above zero at least once during the first seven days of illness: think clearly (90%), speak clearly (83.5%), sleep well (91.3%), breathe easily (95.7%), accomplish daily activities (90.0%), interact with others (87.8%), and live your personal life (88.7%). The WURSS uses "very mild" as a response option. Frequency of items rated as mild, moderate or severe were somewhat lower.
Figure shows daily change over time of illness severity as measured by the WURSS-21, the WURSS-44, the Jackson scale, and the SF-8 (both physical and mental health scores). Sample size decreases as participants report resolution of their illnesses, from N = 230 on Day 1 to N = 100 on Day 12, as only those with continuing colds are included. Day-to-day change would appear even more dramatic if those reporting resolution of illness were included in these figures. As measured by the SF-8, general physical health is impaired more and recovers more swiftly than mental health during common cold illness. Illness-specific health changes more rapidly than general health, whether measured by Jackson symptoms or by either version of WURSS. All changes are more rapid in the first several days than later on.
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.
Figure shows scatterplot correlations of the WURSS-21 and WURSS-44 with SF-8-assessed general physical and mental health, and with the Jackson score. Illness-specific health-related quality-of-life (WURSS) correlates more closely with physical than mental health, as expected. Jackson symptoms also correlate more strongly with SF-8 physical than mental health. Both versions of WURSS associate more strongly with Jackson and SF-8 than those two measures do with each other. Not unexpectedly, the strongest associations observed were the WURSS-21 with its parent WURSS-44, yielding Pearson correlation coefficients of 0.920, 0.925, and 0.937 on Days 2, 3 and 4, respectively. Together, we interpret these findings as evidence of convergent validity.
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, (more ...)
Tables and present item-by-item evaluation criteria for the WURSS-44 and WURSS-21. Each item is portrayed in terms of frequency, severity, minimal important difference (MID), mean squared error (MSE), used to generate Guyatt's responsiveness coefficient. Coefficients representing these criteria are strikingly similar to those in the first WURSS validation study[24
]. WURSS-21 items also appear to perform similarly when included in the WURSS-44, and when rated separately in the short form WURSS-21. In general, items included in the WURSS-21 demonstrate greater responsiveness than the WURSS-44 items not included in the 21-item version. One exception is that WURSS-44 items #13 (feeling "run down") and #32 (lack of energy) perform very well, but are not included in the WURSS-21. When similar findings were noted in the first validation study, we decided not to include these in the short form WURSS-21 because of excessive overlap (redundancy) with item #18 (feeling tired). The instruments as a whole yielded similar MIDs and responsiveness indices to the first study,[24
] with MID and responsiveness index of 18.5 and 0.75 for the WURSS-44, and 10.3 and 0.71 for the WURSS-21 in the current study, compared to 16.7 and 0.71 for the WURSS-44 and 9.48 and 0.80 for the WURSS-21 (as 19 items embedded in the WURSS-44) in the first study[24
Frequency, severity, importance, minimal important difference and responsiveness of WURSS-44 Items
Frequency, severity, minimal important difference, and responsiveness of WURSS-21 Items
Arguably, importance-to-patients may be the most valuable criteria for determining which items should be included in any health-assessing questionnaire. Analysis of responses regarding importance confirmed and extended the findings from our previous WURSS validity study. Mean importance of items ranged from 2.77 (watery eyes) to 4.59 (sleep well) on a 1 to 5 scale, with very similar patterns to those found in the first study. Another previously noted finding is that functional quality-of-life items tend to be rated as more important than items rating symptoms. Among symptom-assessing items, the more frequent (nasal, sore throat, cough, head congestion, chest congestion) tend to be rated as more important than those less frequent (sweats, chills, swollen glands, eye symptoms). Overall, the majority of WURSS items, especially those selected for the WURSS-21, were rated as at least "somewhat important" by most of the people most of the time.
Tables , and show the results of factor analysis for the WURSS-44, and tables , and display corresponding results for the WURSS-21. Exploratory analysis began with Day 3 data, chosen because this day represents the breadth of symptomatic and functional impairment as well or better than any other day. Factorial structures were fit allowing for three to 43 dimensions for the WURSS-44. Very little added explanatory power was found for models with nine or more dimensions, hence we settled on an eight dimension model. For the WURSS-21, a 3-dimensional structure was chosen, after looking at fit indices for models with two to 20 dimensions. Tables and show additional coefficients for the models selected, as well as indicators of how these factorial models play out over time. Fit indices for both instruments are strong, easily meeting criteria suggested by Hu and Bentler[58
]. Tables and show individual items in the dimensional structures, along with indicators of reliability. Reliability coefficients derived by methods of Joreskog[51
] and Bollen[52
] were all significant at p < 0.01 using Wald testing[55
Model fit Exploratory Factor Analysis for WURSS-44 using 3 to 10 dimensions
Best fit factorial model for WURSS-44
Best fit factorial model for WURSS-44
Model fit EFA for WURSS-21 using 2 to 7 dimensions
Best fit factorial model for WURSS-21
Best fit factorial model for WURSS-21
Table displays estimated sample size for two-armed randomized trials, using data gathered here, and common statistical assumptions used in power studies. Powering a common cold treatment trial on MID and responsiveness makes most sense when the therapy is hypothesized to influence the rate of recovery, and when trialists prefer to study participants for a week or less. The main limitation is that MID and daily change rates are neither intuitive nor supported by theory as primary outcomes. Powering a trial on area-under-the-curve makes more sense from a theoretical perspective, as overall illness-related quality-of-life is an intuitively understandable and conceptually consistent primary outcome. For the sample described here, mean AUC for the WURSS-21 was 310.1 with standard deviation 251.0. Corresponding values for the WURSS-44 were mean 570.6 and SD 504.5.
Sample size for powering trials using WURSS-21 and WURSS-44