Data analyses will be performed by the SPSS for Windows® (release 17.0, SPSS Inc., Chicago, IL, USA). Descriptive statistics will be carried-out for all outcome variables. Differences between the groups at baseline will be investigated with the independent Student's t-tests for all variables related to the demographic and clinical characteristics. If differences between the groups at baseline exist, analysis of covariance will be used to eliminate the influence of extraneous factors.