Asthma severity: a factor analytic investigation

Reviewers of the asthma research literature have called for improved questionnaires and other measures, particularly for assessing the severity of asthma. To help meet this need, standard multivariate and psychometric techniques were used with data from asthma patients to develop and evaluate a series of scaled questions. Since there is no "gold standard" for assessing asthma severity, we hope this analysis will help improve our ability to more precisely define these important parameters.

Data were collected through interviews and review of clinic records for 199 adult patients with asthma from a university clinic population. For evaluating the severity of asthma, eight scales assessed asthma duration, the incidence of asthma symptoms, the extent to which asthma is an inconvenience to patients, the incidence of respiratory diseases, medication regimens, medication side effects, and health care utilization. Forced expiratory volume in 1 second as a percentage of predicted normal was included as an objective measure of pulmonary function. A physician rating scale assessed the severity of the underlying disease, not the severity of a particular episode, as either (1) mild (infrequent attacks with interim symptomatic treatment), (2) moderate (more frequent attacks with continuous daily treatment), and (3) severe (continuous symptom with continuous multiple drug regimen, including some systemic steroids).

In the current analysis of data from adult asthma patients, the scales correlated positively with a physician judgment scale. Factor analysis with an oblique rotation yielded three factors that provided a concise summary of asthma severity. We have named the factors (A) Symptom Intensity, (B) Airflow Impairment, and (C) Management Intensity.

Asthma severity appears to be multidimensional rather than unidimensional, including at least three components. The physician rating scale, in combination with measures of the three identified factors, could easily be included in other asthma research protocols to provide a standard, brief assessment of asthma severity and might thus promote greater comparability among studies.