Seasonality, ambient temperatures and hospitalizations for acute exacerbation of COPD: a population-based study in a metropolitan area

Almagro, Pere; Hernandez, Carme; Martinez-Cambor, Pable; Tresserras, Ricard; Escarrabill, Joan

Continuous variables are expressed as the mean ± standard deviation while categorical variables are described by absolute and relative frequencies. Means among seasons were compared using the Welch robust test. Fisher's Exact test of proportions was used to compare the influence of different factors on the proportion of hospitalizations. Simple and multivariate linear regression models were used to investigate the relationship between the different variables (measured in weekly means) and the total number of weekly hospital admissions for COPD. Multicollinearity of the multivariate models was checked using Durbin-Watson tests. The real shape of the model was previously investigated by a general additive model. The determination coefficient was used to measure the quality of the models. P-values below 0.05 were considered to be statistically significant. All calculations were performed with the R.2.10 free software package (www.r-project.org).