John Kennedy of the University of Kansas and Shi Yaojiang of Shaanxi Normal University have released a study claiming that the births of many of the girls may, in fact, simply not have been registered.

“People think 30 million girls are missing from the population. That’s the population of California, and they think they’re just gone,” said Kennedy, an associate professor of political science, according to the university website.

“Most people are using a demographic explanation to say that abortion or infanticide are the reasons they don’t show up in the census and that they don’t exist. But we find there is a political explanation.”

Local officials, they argue, were complicit in the concealment to retain support from villagers, and maintain social stability.