Affiliations: Hospital Universitario Juan Canalejo A Coruña, Spain,
Santiago de Compostela University Santiago de Compostela, Spain,
University of California, San Francisco San Francisco, CA
Correspondence to: Marina Blanco-Aparicio, MD, Hospital Universitario Juan Canalejo, Pneumology, Xubias Arriba, 84, A Coruña 15006, Spain; e-mail: email@example.com
We have read with interest the recently published article by Chen et al in CHEST (June 2006)1warning about the potential problems of the response format of the airways questionnaire 20 (AQ20). The original AQ20 was a simple, reliable, and valid instrument,2–4 which allowed the following three possible responses: “yes”; “no”; and “not applicable” (with a score of 0 for the answer “not applicable,” which is equivalent to “no”). Patients with the greatest disability were more likely to respond “not applicable,” yielding a lower total score and, then, underestimating actual impairment.5
In order to correct this drawback, the authors modified seven activity-based items (items 3, 4, 10, 11, 12, 13, and 14) to include an “unable” response that was given a score of 1 (equivalent to “yes”). Only a minority of subjects (5.9%) in this study endorsed the “unable” response in these items. Nevertheless, neither in this work nor in previous literature2–4 has the number of subjects who choose the option “not applicable” been reported.
In our Spanish validation study of the AQ20,6 in a sample of 208 patients with asthma and COPD we detected a high percentage of subjects who answered “not applicable,” particularly in two of the items modified by Chen et al1 (item 3, 43%; item 11, 56%). Choosing this response does not relate to the degree of impairment measured by the following other parameters: dyspnea MRC; FEV1 percent predicted; illness severity, according to the Global Initiative for Asthma classification for asthma and the Global Initiative for Chronic Obstructive Lung Disease classification for COPD; the St. George Respiratory Questionnaire; the Juniper asthma quality of life questionnaire; the chronic respiratory disease questionnaire; and the short form-12 questionnaire (p > 0.05).
These results suggest that, despite the inclusion of the “unable” option, items 3 and 11 could also be representing a high rate of “not applicable” responses, so further studies are needed to investigate this subject in more detail.
The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
NA = not applicable.
We appreciate the insightful comments provided by Blanco-Aparicio and Vázquez1 regarding our recent article in CHEST (June 2006). We agree that the frequency of “not applicable” responses is an interesting question. Among the seven modified items (n = 352 subjects), 391 of the 2,464 responses were “not applicable.” As reported in our original article,,1 there were 39 “unable” responses. Thus, of all non-“yes/no” responses to the modified items nearly 10% were “unable.” Since we did not coadminister the Airways Questionnaire 20 (AQ20) and AQ20-revised, it is not possible to determine what proportion of subjects who responded “unable” would have chosen “not applicable” in the original format.
Consistent with the findings of Blanco-Aparicio and Vázquez,1we observed a higher frequency of “not applicable” responses for item 3 (“gardening”) and item 11 (“activities at work”) relative to the other five modified items (Table 1
). In addition, we also observed a high frequency of “not applicable” responses for item 14 (“a night out”). The high frequency of “not applicable” responses to these items, despite the inclusion of the “unable” option, suggests that the activities queried by these items may in fact be less relevant to the study population. In a recent publication by Barley and Jones,2 Rasch analysis was used to assess the measurement properties of the AQ20 over time. Item 3 was found to be unstable due an increase in “not applicable” responses related to seasonal changes over the study period. The variable relevance of these items to subjects, rather than the inability to perform these activities, may explain the lack of correlation between “not applicable” responses and other health status measures noted by Blanco-Aparicio and Vázquez. Nonetheless, we believe that providing an “unable” response option further minimizes the potential for any misclassification, particularly among those subjects with a high degree of respiratory impairment.
We agree with the final conclusion of Blanco-Aparicio and Vázquez1 that additional studies of this question are needed.
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