 This resulted in lower fertility rates causing the Baby Bust.Jan Van Bavel and David S. Reher proposed that the increase in nuptiality (marriage boom) coupled with low efficiency of contraception was the main cause of the baby boom.They doubted the explanations (including the Easterlin hypothesis) which considered the post-war economic prosperity that followed deprivation of the Great Depression as main cause of the baby boom, stressing that GDP-birth rate association was not consistent (positive before 1945 and negative after) with GDP growth accounting for a mere 5 percent of the variance in the crude birth rate over the period studied by the authors.