The association between
GSTM1 or
GSTT1 polymorphism and senile cataract was estimated by calculating pooled ORs and 95% CIs. The significance of the pooled OR was determined by
Z test (
P < 0.05 was considered statistically significant). The
I 2-based Q statistic test was performed to evaluate variations due to heterogeneity rather than chance. A random-effects (DerSimonian-Laird method
17 ) or fixed-effects (Mantel-Haenszel method
18 ) model was used to calculate pooled effect estimates in the presence (
P ≤ 0.10) or absence (
P > 0.10) of heterogeneity. Begg's funnel plot, a scatter plot of effect against a measure of study size, was generated as a visual aid to detecting bias or systematic heterogeneity.
19 An asymmetric funnel plot indicated a relationship between effect and study size, which suggested the possibility of either publication bias or a systematic difference between smaller and larger studies (small study effects). Furthermore, publication bias was assessed by Egger's test
20 (
P < 0.05 was considered statistically significant). Studies were categorized into subgroups based on ethnicity, sex, and subtypes of senile cataract, and data analysis was performed (STATA, version 10; StataCorp LP, College Station, TX).