Statistical analysis
The chi-square test and Student’s t-test were used for comparison of categorical and continuous variables, respectively. Levene’s test was used to check the homogeneity of variance; equivalent non-parametric tests were used when Kolmogorov–Smirnov was in favour of the absence of normal distribution. Results with P < 0.05 were regarded as significant. PASW Statistics version 18.0 was used for descriptive and inferential statistical analysis.