The Easterlin effect.

"The Easterlin effect posits cyclical changes in demographic and social behavior as the result of fluctuations in birth rates and cohort size during the post-World War II period.... The Easterlin effect has generated a large literature in the several decades since it was first proposed. Our review of the empirical studies notes the diversity of support across behaviors, time periods, and nations.... Our review emphasizes both the contingent nature of the Easterlin effect and the way in which conditions have changed in recent decades to reduce the salience of cohort size for social and demographic behavior."