title: Assessment of the internal structure of GOLD 2011 system.
abstract: BACKGROUND
  Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2011 introduced a new multidimensional system (symptom/risk) for assessment chronic obstructive pulmonary disease (COPD). The aim of this study was to explore the construct validity of the GOLD 2011 classification strategy; specifically, we evaluated its internal structure in terms of reliability and exploratory factor analysis (EFA).
  
  
  METHODS
  Reliability (Cronbach alpha coefficient), correlations between variables and two successive EFA were performed to assess the internal structure of GOLD 2011. Symptoms (mMRC dyspnea score) and risk (number of previous year exacerbations and forced expiratory volume in the first second % of predicted) were selected as variables.
  
  
  RESULTS
  The analysis included 679 COPD patients from two Spanish cohorts (71.4 ± 11.7 years). Alpha coefficient of the 3 items was 0.52 for the whole sample. Variables presented statistically significant correlations, but of low to moderate magnitude. A first EFA extracted only one factor accounting 52% of the total variance. A second EFA including four items (the three GOLD 2011 variables plus comorbidities as Charlson index score), extracted two-factors accounting for 65% of the total variance. The first factor included the three items of GOLD 2011, and the second contained only one variable (comorbidities). This solution was stable in patients with different levels of COPD severity.
  
  
  CONCLUSIONS
  The available evidence suggests that GOLD 2011 strategy presented a low reliability, and its theorized multidimensionality was not confirm by EFA. Comorbidities appears as a separate and independent domain.
authors.affiliation: Departamento de Emergencia, Hospital Central de las Fuerzas Armadas, Av. 8 de Octubre 3020, Montevideo 11300, Uruguay. Electronic address: gustavo.javier.rodrigo@gmail.com.
authors.forename: Gustavo J
authors.initials: GJ
authors.lastname: Rodrigo
authors.affiliation: Servicio de Neumología, Hospital Arnau de Vilanova, C/San Clemente, 12, 46015 Valencia, Spain. Electronic address: JJSOLER@telefonica.net.
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Soler-Cataluña
authors.affiliation: Servei de Pneumologia, Hospital de la Santa Creu i Sant Pau. Departament de Medicina, Universitat Autonoma de Barcelona. Avda. Institut d'Investigació Biomédica Sant Pau (IIB Sant Pau), Sant Antoni M. Claret 167, Barcelona 08005, Spain. Electronic address: isolanes@santpau.cat.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Solanes
authors.affiliation: Department of Clinical Epidemiology and Public Health, Hospital de la Santa Creu i Sant Pau, Biomedical Research Institute Sant Pau (IIB Sant Pau), Autonomous University of Barcelona, CIBER Epidemiology and Public Health (CIBERESP), Sant Antoni Mª Claret 167, 08025 Barcelona, Spain. Electronic address: ibolibar@santpau.cat.
authors.forename: Ignasi
authors.initials: I
authors.lastname: Bolibar
authors.affiliation: EAP Encants, CAP Maragall, Catalan Health Institute, Barcelona, Spain. Electronic address: mallauger@gencat.cat.
authors.forename: Ma Antònia
authors.initials: MA
authors.lastname: Llauger
authors.affiliation: Servei de Pneumologia, Hospital de la Santa Creu i Sant Pau. Departament de Medicina, Universitat Autonoma de Barcelona, Avda, Institut d'Investigació Biomédica Sant Pau (IIB Sant Pau), Sant Antoni M. Claret 167, Barcelona 08005, Spain. Electronic address: vplaza@santpau.cat.
authors.forename: Vicente
authors.initials: V
authors.lastname: Plaza
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004417:Dyspnea / Q000209:etiology* / Q000503:physiopathology; D005163:Factor Analysis, Statistical; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000145:classification* / Q000503:physiopathology; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013030:Spain
keywords: Assessment; Chronic obstructive pulmonary disease; GOLD