FIGURE 1
SYMPTOMS REPORTED IN INDIVIDUAL INTERVIEWS
FIGURE 2
ITEM FORMAT FOR THE WISCONSIN UPPER RESPIRATORY SYMPTOM SURVEY
Discussion
Researchers of URIs and the common cold need a well-developed, standardized, validated outcomes instrument that reflects the experience and values of cold sufferers. While the Jackson scale and various modifications have been widely used, few data support the validity of these scales. Although correlations with external measures, such as physical examinations, mucus weight, and the ability to culture virus have been reported, the symptomatic and functional impact of colds has largely been neglected. Perhaps more important, the symptomatic measures used to date were apparently developed without significant input from the people whose illnesses were measured. Questionnaire development and cognitive testing methods have not been described, nor have adequate tests of psychometric properties been reported. Although the Jackson scale may demonstrate marginal face validity in terms of symptoms, it does not do so in terms of functional impact.
This article describes the first steps taken in the development and validation of a new illness-specific quality-of-life instrument for measuring the common cold. The WURSS instrument is more comprehensive than existing alternatives and better reflects cold-sufferers’ experiences and values. Therefore, it provides greater face validity. The length (44 items) reflects a compromise between ease of use and comprehensiveness.41 It is possible that a subset of the items will prove nearly as effective and that a short-form WURSS will eventually be available. Item reduction will need to be guided by both internal (factor analysis) and external (frequency and perceived value) considerations. The standardized 7-point severity scale used throughout the WURSS makes the instrument very easy to use.49 It also provides a severity range that our informants and previous researchers40,63,64 agree is optimal. The WURSS allows a cold-sufferer to swiftly and accurately assess his or her common cold. We hope that WURSS will prove worthy in terms of standard psychometric properties such as precision, reliability, and responsiveness.65-68 A large prospective study will be necessary for those assessments.
Limitations
The work described here has a number of limitations. The WURSS was developed in Madison, Wis., largely among people with self-diagnosed colds during the period from July to December 2000. The RCT occurred over several months in the spring of 1999 and was limited to college students. Our results are therefore limited by both population and etiologic agent, which in turn may influence the symptom and severity spectrums assessed. Although we aimed for and achieved a moderate degree of socioeconomic diversity (Table 3), our participants’ responses may not be representative of the larger universe of cold-sufferers. The symptom distribution in Figure 1, for example, is unlikely to represent global cold symptom frequency accurately. Previous research with both natural and induced colds suggests that nasal symptoms and sore throat are usually more frequent than cough.2,3,6-18 The comprehensiveness of the instrument is more important for instrument development than are the specific item frequencies. Here, we feel that we succeeded in representing a sufficient range of items.
Another important limitation is the inherent variability and subjectivity of information generated from qualitative research. A similar instrument development effort carried out by different researchers would inevitably yield a somewhat different questionnaire. Eliciting and formatting terminology that reflects symptomatic and functional impact presents a number of challenges. Future research could employ a quantitative importance scale for participants to use in assessing the value of symptoms and functional impacts. Such value scales could be used alongside factor analysis models of item and dimension frequency and severity. These could in turn be compared with external criteria such as physician assessment, tissue counts, and nasal mucus weights, measurements of inflammatory cytokines, and quantitative viral cultures. Because no gold standard exists, single-criterion validity assessment will not be sufficient. Instead, the concept of construct validity will need to be invoked for future attempts at validation. Construct validity has been defined as “validity assessed by comparing the results of several contrasting tests of validity (including concurrent, convergent, and divergent validation studies) with predictions from a theoretical model.”64 Our work so far has only begun to scratch the surface of such rigorous validity assessment.
Conclusions
We have developed an instrument that measures patient-oriented outcomes identified as important by people with self-diagnosed common colds. We expect that the WURSS will do well with physician-diagnosed “bronchitis,” “sinusitis,” or “pharyngitis,” but as yet have no data with which to evaluate that supposition. We hope that the development of the WURSS stimulates other researchers to undergo similar efforts at aimed at patient-oriented outcome measurement and that the efforts can be compared. We have made the WURSS available for general use by placing a printable facsimile online at http://www.fammed.wisc.edu/wurss/. University-based health care researchers and other nonprofit entities may use the WURSS freely, but we do ask to be notified of such use. For-profit entities should contact us before using this copyrighted instrument.