Cai is a social demographer, specializing in Chinese demography in a global context of low fertility and rapid aging. In a recent paper titled “China’s New Demographic Reality,” published in Population and Development Review, he documents the drastic demographic changes in China between 2000 and 2010, and shows that China has entered a new demographic era characterized by prolonged low fertility, elevated sex ratios, rapid aging, fast urbanization, and major geographic redistribution. His research has attracted both academic and public attentions, including reports in Science, The New York Times, and The Wall Street Journal, among others.