A 2026 working paper from the National Bureau of Economic Research (NBER) pointed out that the total fertility rate in the United States has dropped by 22% since 2007, and this decline cannot easily be explained by common factors such as the economic situation, contraceptive use, housing or childcare costs. The study authors turned to a different shock: the popularity of smartphones, particularly the iPhone, the first generation of modern smartphones.
They used AT&T mobile broadband coverage as a natural experiment to identify the impact of the iPhone on fertility, taking advantage of the unique period when the iPhone was only sold on the AT&T network between June 2007 and February 2011.
The study pieced together county-level data into a panel from 2003 to 2011, combining county-by-county AT&T, Sprint, T-Mobile and Verizon mobile broadband coverage with birth data grouped by age. The authors focused on comparing counties with almost full coverage by AT&T and counties with almost no coverage, because during the period when the iPhone was exclusively sold, "functional use" of the iPhone depended on access to AT&T's mobile broadband network. The study adopted two methods: one is entropy balanced Poisson event study, and the other is synthetic difference in difference (SDID), both of which are used to eliminate systematic differences between the treatment group and the control group in urbanization, race, political orientation, etc.
The results showed that the proliferation of iPhones was significantly associated with a decline in the birth rate of young women. Among women aged 15 to 19, the study estimated a decline in birth rates of 4.5% to 8.0% and among women aged 20 to 24, a decline of 3.2% to 6.6%. There was also a decline among older age groups, but the magnitude was smaller and some results were not statistically significant. Calculated on a national county scale, the authors believe that the spread of iPhones can explain 33% to 52% of the decline in the total fertility rate for women aged 15 to 44 in the United States since 2007.
The authors also used national survey data to verify possible mechanisms, and the results are consistent with the explanation that "iPhones reduce face-to-face interactions, increase pornography use, and reduce sexual frequency." The paper mentioned that behavioral research around mobile phones and social media has found that young people in the smartphone era spend less time in face-to-face socializing, dating, drinking, driving, etc., and at the same time, the number of sexual partners and the frequency of sexual life are also declining. The study therefore believes that the iPhone does not simply change the communication tool, but changes the time allocation and socialization style of young people, thus having a measurable impact on fertility behavior.
The iPhone and the smartphone era it ushered in have essentially accelerated the downward fertility trend in the United States that has continued since 2007. The authors emphasize that this conclusion does not mean that mobile phones are the only cause, but it provides a quantitative explanation for the decline in birth rates, especially among young women. This study advances the previous academic observation that "smartphones have changed the lifestyle of young people" to a clearer level of causal identification.
learn more:
https://www.nber.org/system/files/working_papers/w35310/w35310.pdf