When results of the subgroup analyses for ER-α XbaI polymorphism were stratified by HWE status of controls, type of disease, ethnicity, and gender, significant associations were observed among the subgroup in which controls are consistent with HWE, chronic periodontitis, female population, and the Chinese Han population; these findings are similar to the overall analysis results of homozygote contrast (XX versus xx) and the recessive genetic model (XX versus Xx+xx) (Table 2). The gene discussed is ESR1; the disease is chronic periodontitis.