Optimal fertility during World War I

During World War I (1914–1918) the birth rates of countries such as France, Germany, the U.K., Belgium and Italy declined by almost 50 percent. The age structure of these countries’ populations were significantly affected for the duration of the 20th century. In France, where the population was 40 millions in 1914, the deficit of births is estimated to 1.36 millions over 4 years while military losses are estimated at 1.4 millions. In short, the fertility decline doubled the demographic impact of the War. Why did fertility decline so much? The conventional wisdom is that fertility fell below its optimal level because of the absence of men gone to war. I challenge this view using the case of France. I construct and calibrate a model of optimal fertility choice where households reaching their childbearing years on the eve of WWI face a loss of husband’s income during the War as well as an increase in the probability that the wife remains alone after the War. I calibrate this probability using the casualties sustained by the French army. The model accounts for 97% of the fertility decline even though it does not feature any physical separations of couples. It also accounts for no less than half of the increase in fertility after the War, and generates a temporary increase in the age at birth as observed in the French data. This effect of the War on the optimal level of fertility is robust to alternative calibrations