Validation of the asthma impact survey, a brief asthma-specific quality of life tool

Validation of an Arabic Version of the Obesity-Related Wellbeing (ORWELL 97) Questionnaire in Adults with Obesity

BACKGROUND

No specific questionnaire that evaluates Health-Related Quality Of Life (HRQOL) in individuals with obesity is available in the Arabic language. The aim of this study was therefore to propose and examine the validity and reliability of an Arabic language version of the ORWELL 97, a validated obesity-related HRQOL questionnaire.

METHODS

The ORWELL 97 questionnaire was translated from English to Arabic language and administered to 318 Arabic-speaking participants (106 from clinical and 212 from community samples), and underwent internal consistency, test-retest reliability, construct and discriminative validity analysis.

RESULTS

Internal consistency and the test-retest reliability were excellent for ORWELL 97 global scores in the clinical sample. Participants with obesity displayed significantly higher ORWELL 97 scores than participants from the community sample, confirming the good discriminant validity of the questionnaire. Confirmatory factor analysis in the clinical sample revealed a good fit for a modified two-factor structure.

CONCLUSION

Overall, the Arabic version of the ORWELL 97 can be considered validated in Arabic adult patients with obesity, paving the way to further assessment of its responsiveness in measuring changes in health-related quality of life associated with obesity treatment.

Perceptions of asthma control in the United Kingdom: a cross-sectional study comparing patient and healthcare professionals' perceptions of asthma control with validated ACT scores

Perceptions of asthma control often vary between patients and physicians. This cross-sectional survey provided UK-specific data on actual and perceived asthma control in patients (18–75 years) attending routine asthma reviews in primary, secondary and tertiary settings. Differences between healthcare professionals’ (HCP) and patients’ perceptions of asthma control were evaluated via an online questionnaire and compared to a control—the validated asthma control test (ACT)—which patients completed. Treated patients (at least a short acting ß-agonist) with a documented diagnosis of asthma were enroled and consented within a month of their last appointment. Patients were grouped according to the British Thoracic Society (BTS)/Scottish Intercollegiate Guidelines Network (SIGN) 2014 treatment guidelines (BTS/SIGN steps 1–5). A total of 260 patients were screened: 234 were eligible for enrolment: 33, 52, 50, 49 and 50 patients in steps 1–5, respectively. Seventy per cent (164) were women. The percentage of patients aged 45–64 years was 47.4%. HCPs classed 70% (164) as non-smokers. 84.2% of patients and 73.9% of HCPs perceived that asthma was controlled but ACT results suggest that asthma was only controlled in 54.7% of patients (ACT score ≥20). Patients in steps 4 and 5 had the highest levels of uncontrolled asthma. Correct agreement between ACT score with perceptions of controlled or uncontrolled asthma occurred in 67.9% of patients and 68.8% of HCPs; the poorest levels of agreement occurred in patients in steps 4 and 5. Uncontrolled asthma is common in UK patients. High proportions of patients and HCPs have incorrect perceptions of asthma control, especially in relation to patients with asthma in steps 4 and 5.

Asthma patients and their doctors often misperceive whether the disease is under control, according to a British study. Andrew Menzies-Gow from Royal Brompton Hospital in London and Gavin Chiu from Boehringer Ingelheim UK in Bracknell used an online questionnaire to assess perceptions of asthma control among 234 patients and their healthcare providers. All participants had at least intermittent asthma that required occasional treatment; many had more severe disease. The researchers found that 84% of patients and 74% of doctors thought the asthma was well controlled, but results of the Asthma Control Test indicated only 55% of patients objectively achieved disease control. Correct agreement between the validated test and more subjective perceptions occurred in only 68 % of patients and 69% of doctors. Addressing this mismatch could go a long way to improving asthma control among British patients.

Mismatching Among Guidelines, Providers, and Parents on Controller Medication Use in Children with Asthma

BACKGROUND

Underuse of controller medicines among children with asthma remains widespread despite national guidelines.

OBJECTIVES

To (1) assess provider prescribing patterns for asthma controller medications; (2) assess how frequently parents' reports of their child's asthma controller medicine use were mismatched with their provider's recommendations; and (3) evaluate parent attitudes and demographic characteristics associated with these mismatches.

METHODS

In this cross-sectional study, we conducted linked surveys of parents and providers of children with probable persistent asthma in a Medicaid program and 4 commercial health plans in 2011. Probable persistent asthma was defined as a diagnosis of asthma and 1 or more controller medication dispensing.

RESULTS

This study included 740 children (mean age, 8.6 years). Providers for 50% of the children reported prescribing controller medications for daily year-round use, 41% for daily use during active asthma months, and 9% for intermittent use for relief. Among parents, 72% knew which class of controller medication the provider prescribed and 49% knew the administration frequency and the medication class. Parents were less likely to report the same controller medication type as the provider, irrespective of dose and frequency, if they were Latino (odds ratio [OR], 0.23; CI, 0.057-0.90), had a household smoker (OR, 2.87; CI, 0.42-19.6), or believed the controller medicine was not helping (OR, 0.15; CI, 0.048-0.45).

CONCLUSIONS

Mismatches between parent reports and providers intentions regarding how the child was supposed to use inhaled steroids occurred for half of the children. Efforts should focus on ways to reduce mismatches between parent and provider intentions regarding controller medication use.

Assessing the validity of the RAND negative impact of asthma on quality of life short forms

BACKGROUND

In response to recommendations from the 2010 National Institutes of Health Asthma Outcomes Workshop, we developed a system for measuring the negative impact of asthma on quality of life (QoL), which was referred to as the RAND Negative Impact of Asthma on Quality of Life (RAND-IAQL) item bank. The bank contains 65 items that focus on the patient's perception of the impact or bother of asthma on his or her life.

OBJECTIVE

Evidence for the validity of 2 short forms, the RAND-IAQL 4-item and 12-item Short Forms, from the bank is presented.

METHODS

Using a sample of 2032 adults with asthma, we validated our short forms against the Asthma Quality of Life Questionnaire-Marks (AQLQ-M), the Asthma Control Test, and generic measures of QoL developed by the Patient-reported Outcomes Measurement Information System (PROMIS). Discriminant validity was examined by comparing scores of respondents who differed according to multiple health indicators.

RESULTS

Our sample ranged in age from 18 to 99 years (mean, 43 years), with 14% Hispanic, 11% Asian, 19% African American, and 56% non-Hispanic white race/ethnicity. Men had a significantly worse impact of asthma on QoL than women. The impact of asthma on QoL was greatest in African American and Hispanic subjects compared with that seen in non-Hispanic white subjects. Our measures correlated highly with the AQLQ-M and more strongly with the PROMIS global physical than mental scales. They differentiated between adults with asthma according to their perceived severity, level of control, presence or absence of exacerbations, and physical comorbidity.

CONCLUSION

The RAND-IAQL item bank, measuring the impact of asthma on QoL, will complement other patient-reported outcomes, such as measures of asthma symptoms, functioning, and control.

Measurement properties of asthma-specific quality-of-life measures: protocol for a systematic review

BACKGROUND

Asthma is a frequent chronic inflammatory disease of the airways, and the assessment of health-related quality of life (HrQoL) is important in both research and routine care. Various asthma-specific measures of HrQoL exist but there is uncertainty which measures are best suited for use in research and routine care. Therefore, the aim of the proposed research is a comprehensive systematic assessment of the measurement properties of the existing measures that were developed to measure asthma-specific quality of life.

METHODS/DESIGN

This study is a systematic review of the measurement properties of asthma-specific measures of health-related quality of life. PubMed and Embase will be searched using a selection of relevant search terms. Eligible studies will be primary empirical studies evaluating, describing or comparing measurement properties of asthma-specific HRQL tools. Eligibility assessment and data abstraction will be performed independently by two reviewers. Evidence tables will be generated for study characteristics, instrument characteristics, measurement properties and interpretability. The quality of the measurement properties will be assessed using predefined criteria. Methodological quality of studies will be assessed using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist. A best evidence synthesis will be undertaken if more than one study have investigated a particular measurement property.

DISCUSSION

The proposed systematic review will produce a comprehensive assessment of measurement properties of existing measures of asthma-specific health-related quality of life. We also aim to derive recommendations in order to help researchers and practitioners alike in the choice of instrument.

TRIAL REGISTRATION

PROSPERO registration number: CRD42014010491.

Correspondence between the RAND-Negative Impact of Asthma on Quality of Life item bank and the Marks Asthma Quality of Life Questionnaire

BACKGROUND

In many research and clinical settings in which patient-reported outcome (PRO) measures are used, it is often desirable to link scores across disparate measures or to use scores from 1 measure to describe scores on a separate measure. However, PRO measures are scored by using a variety of metrics, making such comparisons difficult.

OBJECTIVE

The objective of this article was to provide an example of how to transform scores across disparate measures (the Marks Asthma Quality of Life Questionnaire [AQLQ-Marks] and the newly developed RAND-Negative Impact of Asthma on Quality of Life item bank [RAND-IAQL-Bank]) by using an item response theory (IRT)-based linking method.

METHODS

Our sample of adults with asthma (N = 2032) completed 2 measures of asthma-specific quality of life: the AQLQ-Marks and the RAND-IAQL-Bank. We use IRT-based co-calibration of the 2 measures to provide a linkage, or a common metric, between the 2 measures. Co-calibration refers to the process of using IRT to estimate item parameters that describe the responses to the scales' items according to a common metric; in this case, a normal distribution transformed to a T scale with a mean of 50 and an SD of 10.

RESULTS

Respondents had an average age of 43 (15), were 60% female, and predominantly non-Hispanic White (56%), with 19% African American, 14% Hispanic, and 11% Asian. Most had at least some college education (83%), and 90% had experienced an asthma attack during the last 12 months. Our results indicate that the AQLQ-Marks and RAND-IAQL-Bank scales measured highly similar constructs and were sufficiently unidimensional for IRT co-calibration. Once linked, scores from the 2 measures were invariant across subgroups. A crosswalk is provided that allows researchers and clinicians using AQLQ-Marks to crosswalk to the RAND-IAQL toolkit.

CONCLUSIONS

The ability to translate scores from the RAND-IAQL toolkit to other "legacy" (ie, commonly used) measures increases the value of the new toolkit, aids in interpretation, and will hopefully facilitate adoption by asthma researchers and clinicians. More generally, the techniques we illustrate can be applied to other newly developed or existing measures in the PRO research field to obtain crosswalks with widely used traditional legacy instruments.

Asthma exacerbations: predisposing factors and prediction rules

PURPOSE OF REVIEW

Asthma is a multifaceted disease that is associated with decreased lung function, multiple symptoms, varying levels of asthma control, and risk of acute exacerbations. The ability to predict the risk of developing acute exacerbations may improve the management of asthmatics and facilitate identification of these patients for interventional studies.

RECENT FINDINGS

Factors that are associated with different manifestations of asthma differ. Biomarkers that are correlated with airways hyper-responsiveness do not necessarily correlate with risk of future exacerbations. Genetic factors that segregate with exacerbation risk are beginning to emerge. Outcome measures that demonstrate predictive validity have been developed and may facilitate patient management and provide novel clinically meaningful endpoints in clinical trials.

SUMMARY

This review will emphasize underlying factors associated with asthma exacerbations and clinical prediction rules that correlate with the risk of developing severe exacerbations of asthma.

Developing an item bank and short forms that assess the impact of asthma on quality of life

The present work describes the process of developing an item bank and short forms that measure the impact of asthma on quality of life (QoL) that avoids confounding QoL with asthma symptomatology and functional impairment. Using a diverse national sample of adults with asthma (N = 2032) we conducted exploratory and confirmatory factor analyses, and item response theory and differential item functioning analyses to develop a 65-item unidimensional item bank and separate short form assessments. A psychometric evaluation of the RAND Impact of Asthma on QoL item bank (RAND-IAQL) suggests that though the concept of asthma impact on QoL is multi-faceted, it may be measured as a single underlying construct. The performance of the bank was then evaluated with a real-data simulated computer adaptive test. From the RAND-IAQL item bank we then developed two short forms consisting of 4 and 12 items (reliability = 0.86 and 0.93, respectively). A real-data simulated computer adaptive test suggests that as few as 4-5 items from the bank are needed to obtain highly precise scores. Preliminary validity results indicate that the RAND-IAQL measures distinguish between levels of asthma control. To measure the impact of asthma on QoL, users of these items may choose from two highly reliable short forms, computer adaptive test administration, or content-specific subsets of items from the bank tailored to their specific needs.

Development of a measure of asthma-specific quality of life among adults

PURPOSE

A key goal in asthma treatment is improvement in quality of life (QoL), but existing measures often confound QoL with symptoms and functional impairment. The current study addresses these limitations and the need for valid patient-reported outcome measures by using state-of-the-art methods to develop an item bank assessing QoL in adults with asthma. This article describes the process for developing an initial item pool for field testing.

METHODS

Five focus group interviews were conducted with a total of 50 asthmatic adults. We used "pile sorting/binning" and "winnowing" methods to identify key QoL dimensions and develop a pool of items based on statements made in the focus group interviews. We then conducted a literature review and consulted with an expert panel to ensure that no key concepts were omitted. Finally, we conducted individual cognitive interviews to ensure that items were well understood and inform final item refinement.

RESULTS

Six hundred and sixty-one QoL statements were identified from focus group interview transcripts and subsequently used to generate a pool of 112 items in 16 different content areas.

CONCLUSIONS

Items covering a broad range of content were developed that can serve as a valid gauge of individuals' perceptions of the effects of asthma and its treatment on their lives. These items do not directly measure symptoms or functional impairment, yet they include a broader range of content than most existent measures of asthma-specific QoL.

Asthma outcomes revisited

PURPOSE OF REVIEW

Asthma outcomes constitute the cornerstone of asthma clinical research. Despite their known importance, it has been difficult for researchers to standardize these outcomes in large part because of the heterogeneity of the disease. This review seeks to provide an overview of recent recommendations for standardization of asthma outcomes in clinical trials, as well as discuss areas of future interest.

RECENT FINDINGS

Several outcome measures have been recommended and are used in evaluating different interventions in asthma clinical trials. Such outcomes include lung function, asthma control measures, symptoms, exacerbations, quality of life, biomarkers, healthcare utilization and cost of care. More recently, recommendations for core measures, supplemental measures and future areas of interest for all future asthma clinical trials have been recommended by the Asthma Outcomes Workshop supported by the National Institute of Health (NIH) and the Agency for Healthcare Research and Quality (AHRQ) in the US.

SUMMARY

Standardization of asthma outcomes allows the comparison of results across multiple studies and centers. The recommendations of the Asthma Outcomes Workshop constitute an excellent first step in standardizing the way in which asthma outcomes are assessed. The asthma research community is now charged with implementing these recommendations and expanding upon them.

Asthma outcomes: quality of life

BACKGROUND

"Asthma-related quality of life" (QOL) refers to the perceived impact that asthma has on the patient's QOL.

OBJECTIVE

National Institutes of Health institutes and other federal agencies convened an expert group to recommend standardized measures of the impact of asthma on QOL for use in future asthma clinical research.

METHODS

We reviewed published documentation regarding the development and psychometric evaluation; clinical research use since 2000; and extent to which the content of each existing QOL instrument provides a unique, reliable, and valid assessment of the intended construct. We classified instruments as core (required in future studies), supplemental (used according to the study's aims and standardized), or emerging (requiring validation and standardization). This work was discussed at an National Institutes of Health-organized workshop convened in March 2010 and finalized in September 2011.

RESULTS

Eleven instruments for adults and 6 for children were identified for review. None qualified as core instruments because they predominantly measured indicators of asthma control (symptoms and/or functional status); failed to provide a distinct, reliable score measuring all key dimensions of the intended construct; and/or lacked adequate psychometric data.

CONCLUSIONS

In the absence of existing instruments that meet the stated criteria, currently available instruments are classified as either supplemental or emerging. Research is strongly recommended to develop and evaluate instruments that provide a distinct, reliable measure of the patient's perception of the impact of asthma on all of the key dimensions of QOL, an important outcome that is not captured in other outcome measures.

Further validation and definition of the psychometric properties of the Asthma Impact Survey

BACKGROUND

The Asthma Impact Survey (AIS-6) is a brief disease-specific quality-of-life instrument with limited published validation data.

OBJECTIVE

To obtain additional validation data and psychometric properties of the AIS-6.

METHODS

In November, 2007, patients with persistent asthma were mailed a survey that included the AIS-6, the mini-Asthma Quality of Life Questionnaire (mAQLQ), and the Asthma Control Test (ACT). Follow-up surveys were sent in April, July, and October 2008. Year 2008 exacerbations and short-acting β-agonist (SABA) dispensings were captured from administrative data.

RESULTS

A total of 2680 patients had complete baseline survey data. Criterion validity was demonstrated by the strong correlations of the AIS-6 with the mAQLQ (r = -0.84 to -0.86); construct validity by significant relationships (P < .0001) of the AIS-6 with mAQLQ domain scores, ACT score, and history of exacerbations; and predictive validity by significant relationships (P < .0001) between AIS-6 scores at the end of 2007 and year 2008 exacerbations and high SABA dispensings. Responsiveness was demonstrated by significant (P < .0001) correlations (r = -0.39 to -0.58) between changes in AIS-6 scores and changes in mAQLQ and ACT scores over time. A preliminary minimally important difference (MID) in AIS-6 was estimated to be 4 by using the mAQLQ MID as an anchor. Excellent internal consistency (α = 0.94) and test-retest reliability (intraclass correlation coefficient = 0.86-0.91) were also demonstrated.

CONCLUSION

The AIS-6 demonstrated good psychometric properties in a large independent sample and could be used to assess asthma-specific quality of life in clinical practice and clinical research.

Acceptance of Asthma Pharmacogenetic Study by Children and Adults

BACKGROUND

Pharmacogenetic testing may change clinical medicine by allowing clinicians to tailor medications based on a patient's genetic makeup, however, these tests must first be validated in large, real-life populations of subjects that include children. A dearth of knowledge exists for whether pediatric populations are as willing as adult populations to provide samples for such studies.

OBJECTIVE

(1) To assess whether pediatric and adult patients with persistent asthma are willing to provide specimens for DNA extraction and genetic studies. (2) To assess whether patients' willingness to provide blood as compared to buccal smear specimens differ.

METHODS

Of 644 patients ages 4-38 years who had three or more prescription fills for inhaled corticosteroids in one year, 60% (385) were randomized to the blood specimen group and 40% (259) were randomized to the buccal smear group in order to study acceptance of different biospecimen collection methods. Research assistants contacted subjects to obtain consent, perform a phone survey, and request a specimen.

RESULTS

There were no baseline differences between subjects randomized to the blood specimen group versus buccal smear group with respect to age, gender, or number of dispensings of inhaled corticosteroids. Of 259 subjects in the buccal smear group, 30% (78) provided samples, and of 385 subjects in the blood specimen group, 16% (60) provided samples. Subjects randomized to the buccal smear group were more likely to provide specimens for genetic study compared to subjects randomized to the blood specimen group (RR 1.21; 95% CI 1.10 - 1.32), even after adjusting for age. Pediatric subjects were more likely to provide specimens for genetic study than adult subjects with 23% (113) of pediatric subjects providing samples and 15% (25) of adult subjects providing samples (p=0.03).

CONCLUSION

Children with asthma are as likely to participate in genetic studies as adults. Both children and adult subjects are more likely to provide buccal smear specimens rather than blood specimens for genetic study.

Asthma self-assessment in a Medicaid population

BACKGROUND

Self-assessment of symptoms by patients with chronic conditions is an important element of disease management. A recent study in a commercially-insured population found that patients who received automated telephone calls for asthma self-assessment felt they benefitted from the calls. Few studies have evaluated the effectiveness of disease self-assessment in Medicaid populations. The goals of this study were to: (1) assess the feasibility of asthma self-assessment in a population predominantly insured by Medicaid, (2) study whether adding a gift card incentive increased completion of the self-assessment survey, and (3) evaluate how the self-assessment affected processes and outcomes of care.

METHODS

We studied adults and children aged 4 years and older who were insured by a Medicaid-focused managed care organization (MCO) in a pre- and post-intervention study. During the pre-incentive period, patients with computerized utilization data that met specific criteria for problematic asthma control were mailed the Asthma Control Test (ACT), a self-assessment survey, and asked to return it to the MCO. During the intervention period, patients were offered a $20 gift card for returning the completed ACT to the MCO. To evaluate clinical outcomes, we used computerized claims data to assess the number of hospitalization visits and emergency department visits experienced in the 3 months after receiving the ACT. To evaluate whether the self-management intervention improved processes of care, we conducted telephone interviews with patients who returned or did not return the ACT by mail.

RESULTS

During the pre-incentive period, 1183 patients were identified as having problems with asthma control; 25 (2.0%) of these returned the ACT to the MCO. In contrast, during the incentive period, 1612 patients were identified as having problems with asthma control and 87 (5.4%) of these returned the ACT to the MCO (p < 0.0001). Of all 95 ACTs that were returned, 87% had a score of 19 or less, which suggested poor asthma control.During the 3 months after they received the ACT, patients who completed it had similar numbers of outpatient visits, emergency department visits, and hospitalizations for asthma as patients who did not complete the ACT. We completed interviews with 95 patients, including 28 who had completed the ACT and 67 who had not. Based on an ACT administered at the time of the interview, patients who had previously returned the ACT to the MCO had asthma control similar to those who had not (mean scores of 14.2 vs. 14.6, p = 0.70). Patients had similar rates of contacting their providers within the past 2 months whether they had completed the mailed ACT or not (71% vs. 76%, p = 0.57).

CONCLUSION

Mailing asthma self-assessment surveys to patients with poorly controlled asthma was not associated with better asthma-associated outcomes or processes of care in the Medicaid population studied. Adding a gift card incentive did not meaningfully increase response rates. Asthma disease management programs for Medicaid populations will most likely need to involve alternative strategies for engaging patients and their providers in managing their conditions.

The relationship between obesity and asthma severity and control in adults

BACKGROUND

The association of obesity with asthma outcomes is not well understood.

OBJECTIVE

The objective of this study was to examine the association of obesity, as represented by a body mass index (BMI) of greater than 30 kg/m(2), with quality-of-life scores, asthma control problems, and asthma-related hospitalizations.

METHODS

The study followed a cross-sectional design. Questionnaires were completed at home by a random sample of 1113 members of a large integrated health care organization who were 35 years of age or older with health care use suggestive of active asthma. Outcomes included the mini-Asthma Quality of Life Questionnaire, the Asthma Therapy Assessment Questionnaire, and self-reported asthma-related hospitalization. Several other factors known to influence asthma outcomes also were collected: demographics, smoking status, oral corticosteroid use in the past month, evidence of gastroesophageal reflux disease, and inhaled corticosteroid use in the past month. Multiple logistic regression models were used to measure the association of BMI status with outcomes.

RESULTS

Even after adjusting for demographics, smoking status, oral corticosteroid use, evidence of gastroesophageal reflux disease, and inhaled corticosteroid use, obese adults were more likely than those with normal BMIs (<25 kg/m(2)) to report poor asthma-specific quality of life (odds ratio [OR], 2.8; 95% CI, 1.6-4.9), poor asthma control (OR, 2.7; 95% CI, 1.7-4.3), and a history of asthma-related hospitalizations (OR, 4.6; 95% CI, 1.4-14.4).

CONCLUSIONS

Our findings suggest that obesity is associated with worse asthma outcomes, especially an increased risk of asthma-related hospitalizations.

Identifying the components of asthma health status in children with mild to moderate asthma

BACKGROUND

Weak and inconsistent correlations between measurements of asthma health status suggest that the disease is composed of nonoverlapping components.

OBJECTIVE

Factor analysis was used to explore the relationships between measures of asthma morbidity and to identify heterogeneous components of asthma health status in children 5 to 12 years old. Results were compared across time (baseline and 48-month visit) and treatment arms.

METHODS

Analyses were conducted in 7 different study windows in a database from a large clinical trial of children with mild to moderate asthma (n = 1041). Measurements of lung function, symptoms, and health care utilization from daily diary cards, serum IgE levels, total eosinophil count, skin test positivity, and airway hyperresponsiveness were included. Data on fractional exhaled nitric oxide and sputum eosinophil cationic protein were included in a subgroup of patients.

RESULTS

In each of the study windows, factor analysis identified 5 factors that explained between 50% and 60% of the common variance. Factors identified included (1) inflammatory markers, (2) symptoms/medication use, (3) asthma exacerbations, and measures of lung function, which subdivided into (4) FEV(1) and forced vital capacity, and (5) bronchodilator response and the FEV(1)/forced vital capacity ratio. Exploratory analyses suggest that fractional exhaled nitric oxide account for the atopy/inflammatory marker factor, and sputum measurements account for a sixth, separate factor.

CONCLUSION

The consistent identification of a 5-factor structure across time and treatment arms suggests that each of these factors provides independent information in the assessment of asthma.