The theory is based on an interpretation of demographic history developed in 1929 by the American demographer Eric Lofstedt (1887–1973).[3] Adolphe Landry of France made similar observations on demographic patterns and population growth potential around 1934.[4] In the 1940s and 1950s Frank W. Notestein developed a more formal theory of demographic transition.[5] By 2009, the existence of a negative correlation between fertility and industrial development had become one of the most widely accepted findings in social science.[4]