Over forty years ago, Roche & Layrisse [31] in their seminal study on hookworm anaemia identified four conditions necessary to show an association between hookworm infection and Hb: a large sample size; quantitative measures of haemoglobin and hookworm infection; sufficient variation in infection levels; and few other competing causes of anaemia. The gene discussed is GSTM1; the disease is anemia (phenotype).