Objectives: The Severe Respiratory Insufficiency (SRI) Questionnaire has recently been developed and validated for the assessment of health-related quality of life (HRQL) in patients with severe chronic respiratory failure resulting from a broad spectrum of underlying disorders. The present study was aimed at reexamining the internal structure of the SRI specifically for chronic obstructive pulmonary disease (COPD) patients.
Study design and setting: Cross-validation was performed in two COPD groups (N=78 and N=84), each receiving home mechanical ventilation in addition to long-term oxygen therapy. The internal consistency reliability was calculated using Cronbach's alpha coefficient. Explorative Factor Analysis was performed followed by Confirmatory Factor Analysis to establish construct validity.
Results: In the total group (N=162) Cronbach's alpha ranged from 0.73 to 0.88. Only one factor could be established which explained 58.5% of the total variance confirming one Summary Scale (SRI-SS). For each of the seven subscales, Confirmatory Factor Analysis revealed two factors, which were substantially correlated (r=0.43-0.80). All scale scores covered a broad range of the questionnaire's scaling range (0-100). The mean SRI-SS score was 52+/-17 indicating a homogenous scaling distribution.
Conclusion: The SRI is a multidimensional and highly specific tool with high psychometric properties for HRQL assessment in COPD patients with severe chronic respiratory failure.