One of the most catastrophic consequences of China’s decades-long one-child policy is said to be the preference to have boys over girls, which resulted in a severe gender imbalance. One study now claims that the gender imbalance is far overblown, because millions of female babies were not reported at birth.

John Kennedy, an associate professor of political science at the University of Kansas, and Shi Yaojiang of Shaanxi Normal University, said the common assertion that between 30 million to 60 million girls in China went “missing” as a result of sex-selective abortion and female infanticide is inaccurate. Instead, as many as 25 million went unreported at birth, but turn up later in official statistics, the study says.

China implemented the one-child policy in 1979 to curb the country’s high birth rate. The policy was officially scrapped last year, as the country grapples with a graying population and ultra-low fertility rate. The one-child policy is thought to be at least partly responsible for over 500 million sterilizations and abortions (paywall). Many parents had second children in secret and suffered extortion or fines for having more than their allotted quota.

Writing in a study published in November in the journal China Quarterly, Kennedy and Shi found that some rural families had girls that were not reported and were tacitly acknowledged by local officials, who turned a blind eye in return for social stability. Kennedy said that many of these girls were not registered at birth, but would later show up in statistics at junior high and marriage age. Over 25 years, as many as 25 million women who are present in later statistics did not “exist” at birth, the researchers said.

For example, when comparing the number of children born in 1990 with the number of 20 year-olds in 2010, they found four million more people in the later cohort, with about one million more women than men.

China’s gender imbalance is blamed for many social problems today, including a surplus of men who are unable to find wives. While Kennedy acknowledges that there is “nothing more socially unstable than a bunch of testosterone with nowhere to go,” the “marriage squeeze” is in fact not as acute as other studies have suggested because of these large numbers of unreported births.