GSTM1 and anemia (phenotype): Specifically, we found that the bias (difference between mean Hb concentrations using the two methods) is similar in 12-month to 17-month and 18-month to 24-month children, but significantly lower than that of children 6–11 months of age; potential explanations of this finding may be that the anaemia prevalence was higher in younger children or that blood collection may be more challenging among very young children.