7. Statistical analysis. All analyses will be performed using statistical analysis software SAS (SAS, 9.1.3 for Windows, Cary, NC: SAS Institute Inc.1989). All individuals enrolled will be included in the analysis. Descriptive summaries will be presented for all the individuals, and for subgroups of individuals. Statistical tests will be carried out for exploratory purposes, as appropriate. The descriptive analysis of nominal/ordinal data will comprise tabulation of frequency and percentages. Chi-square test (or Fisher exact test in the presence of small frequencies) will be used to compare categories. The descriptive analysis of continuous data will comprise the mean, standard deviation, median, extreme values, and 95% confidence interval. OHS patients will be randomized to receive a short term supplementation of PRFs or placebo (J Nutr 2008), following the scheme of a controlled randomised double-blind clinical trial. POAF occurence will be compared in PRFs supplemented and control groups to assess the efficacy and safety of the intervention. The "intention to treat" principle will be adopted for the analysis of the combined endpoints.