The presence or absence of any anaemia as a binary variable (Hb < 11.5 g/dl), and as an ordinal categorical variable was based on varying degrees from mild (11 < Hb < 11.5 g/dl) to severe (Hb < 8 g/dl) using the WHO cut-offs for children aged 5–11 years old (WHO 2011). This evidence concerns the gene GSTM1 and anemia (phenotype).