Jan Willem Nienhuys (born 16 April 1942) is a Dutch mathematician, book translator and skeptic.

[1] Nienhuys studied mathematics in the Netherlands, and in 1966/67 at Tulane University in New Orleans, where he met his future wife.

This mathematical model would serve as proof that a connection existed between the order of birth and intelligence to the advantage of the firstborn, as Lillian Belmont and Francis A. Marolla concluded in 1973 from a registration of the Dutch armed forces.

This record consisted of the data of nearly 400,000 19-year-old men born in the period 1944–1947, originally collected to investigate the effects of the Hunger Winter (1944–1945) on mental and physical development.

[11][12] On 4 October 2014, Nienhuys received the Gebroeders Bruinsma Erepenning, an award of the Vereniging tegen de Kwakzalverij.