2.3. Statistical analysis

Continuous data are expressed as mean ± standard deviation, and the categorical data are expressed as number (percentage). Comparisons of differences in categorical date between groups were performed using the Chi-square test. Distributions of continuous variables were analyzed by the Student t test or Mann–Whitney U test for the 2 groups where appropriate. Missing data were presented in tables when appropriate. Independent factors possibly affecting 25 (OH)D concentration (cut off value of 20 ng/mL) were determined by stepwise multiple logistic regression analysis.

Hardy–Weinberg equilibrium for each SNP was compared using the Pearson chi-square test (X²). 25 (OH)D concentration and the variance in each genotype was accessed in one-way ANOVA with Bonferroni correction. At univariate analyses, P-value were considered significant when P�<�.2 and in multivariate analyze P�<�.05. All the tests were performed with IBM SPSS Statistics 20.0 for Windows (Chicago, IL).