This was based on his research of British Army records from the First World War, which showed that "surviving soldiers were on average more than one inch (3.33 cm) taller than fallen soldiers".[3] Valerie Grant attributed it to changing hormone levels of women during war, as they tended to "adopt more dominant roles".[5][6] William H. James writing in 2008 gave an increase in coital rates by returning soldiers as a possible cause. He also noted that a fall in the ratio of male births had been recorded in Iran following the Iran–Iraq War, "explained by psychological stress causing pregnant women disproportionately to abort male fetuses".[7]