It is 5 years since the development and first validation of the COPD Assessment Test (CAT) [1], so the review of papers concerning the CAT by Gupta et al. [2] in this issue of the European Respiratory Journal is very timely. The authors identified over 40 studies using a systematic approach to minimise biases, although they acknowledge that they introduced one bias by selecting papers published only in English, French and Spanish, so eight papers were excluded. That may not be too problematic, as the included papers report data on over 25 000 patients from 35 countries across five continents (none from Australasia or Antarctica).
One of the strengths of a systematic review is that it can allow comparison of variability in outcomes across different studies. To this end, the data extracted for this review provide an indication of the reliability of the CAT in different settings, and it is generally very good. For example, the internal consistency measured using Cronbach’s alpha was in the range 0.85–0.98 across nine studies. This observation is important because the CAT was developed in English but these studies included Arabic-speaking countries, Brazil, Greece, Japan, South Korea and Turkey. This observation supports the finding by Kwon et al. [3], in a direct comparison, that the relationship …
