Looking more closely, the actual mean Hb for a group reported as “<5 g/dL” was often between 3–4 g/dL, and the actual mean Hb for a group “>5 g/dL” was often between 5–6 g/dL, as many of the included studies involved patients admitted to a hospital for severe anemia. This evidence concerns the gene GSTM1 and anemia (phenotype).