Establishing measurement invariance: English and Spanish Paediatric Asthma Quality of Life Questionnaire.

BACKGROUND: Registered nurses and nurse researchers often use questionnaires to measure patient outcomes. When questionnaires or other multiple-item instruments have been developed using a relatively homogeneous sample, the suitability of even a psychometrically well-developed instrument for the new population comes into question. Bias or lack of equivalence can be introduced into instruments through differences in perceptions of the meaning of the measured items, constructs, or both in the two groups. OBJECTIVE: To explain measurement invariance and illustrate how it can be tested using the English and Spanish versions of the Paediatric Asthma Quality of Life Questionnaire (PAQLQ). METHODS: A sample of 607 children from the Phoenix Children's Hospital Breathmobile was selected for this analysis. The children were of ages 6-18 years; 61.2% completed the PAQLQ in Spanish. Testing measurement invariance using multiple-group confirmatory factor analysis, a series of hierarchical nested models, is demonstrated. In assessing the adequacy of the fit of each model at each stage, both χ2 tests and goodness-of-fit indexes were used. RESULTS: The test of measurement invariance for the one-factor model showed that the English and Spanish versions of the scale met the criteria for measurement invariance. The level of strict invariance (equal factor loadings, intercepts, and residual variances between groups) was achieved. DISCUSSION: Confirmatory factor analysis is used to evaluate the structural integrity of a measurement instrument; multiple confirmatory factor analyses are used to assess measurement invariance across different groups and to stamp the data as valid or invalid. The PAQLQ, a widely used instrument having evidence to support reliability and validity was used separately in English- and Spanish-speaking groups. Traditional methods for evaluating measurement instruments have been less than thorough, and this article demonstrates a well-developed approach, allowing for confident comparisons between populations.

Confirmation of the validity of the HAQ-DI in two populations living with chronic illnesses.

The assessment of functional health in chronic illnesses such as HIV/AIDS and rheumatoid arthritis is central to the measurement of health-related quality of life. The purpose of this article is to report the testing and comparison of the measurement structure of the Health Assessment Questionnaire-Disability Index (HAQ-DI), a measure of functional health, in 917 persons living with HIV/AIDS and 901 individuals with rheumatoid arthritis. The samples come from data collected as part of the Arthritis, Rheumatism, and Aging Medical Information System (ARAMIS) and AIDS Time-Oriented Health Outcome Study (ATHOS) projects. Using confirmatory factor analysis (CFA), the hypothesized structure represented by a general factor (functional health) and eight measured items was tested separately. Based on the fit indexes, the model fit the ATHOS data (chi2 = 36.933, p < .0117; CFI = 1.000; SRMR = 0.025). After correlating the error terms for two of the measured items, the model also fit the ARAMIS data (chi2 = 302.34, p = .0000; CFI = 0.937; SRMR = 0.041). This analysis provides further support of the construct validity of the HAQ-DI for persons living with HIV/AIDS or rheumatoid arthritis.

Development of a model to measure symptom status in persons living with rheumatoid arthritis.

BACKGROUND: Rheumatoid arthritis (RA) is a chronic illness with a constellation of symptoms. The management of which is important for quality of life. Our review of the literature indicated that there is currently no standardized approach to measuring the symptom status of persons living with RA. OBJECTIVE: The purpose of this study is to report the development and initial validation of a structure to measure symptom status in persons living with RA. METHODS: For this secondary analysis, there were 901 female patients with complete symptom checklists available from the Arthritis, Rheumatism, and Aging Medical Information System. A tentative structure using exploratory factor analysis was developed, the structure was replicated in a separate sample using confirmatory factor analysis, and then hypothesized relationships with an external criterion (functional health) was tested using structural equation modeling. The symptom checklist contains 31 symptoms. The stem question is, "Have you had any of the following symptoms during the past 6 months; if yes mark all that apply." RESULTS: A two-factor structure for measuring symptom status was identified, RA Pain Symptoms and General Symptoms. Using the external criterion, we also demonstrated that the two factors were different and that the RA Pain Symptoms Factor had a stronger impact on functional health. This provides evidence of the discriminant as well as predictive validity of the RA Pain Symptoms Factor. DISCUSSION: Effective symptom management is an important outcome for nursing practice. Because the assessment of symptoms is the first step in symptom management, the identification of a measurement structure is an essential step.