The first results from an ongoing child development study in China show wide disparities between rural and urban children in both living conditions and development outcomes such as physical health and social and emotional well-being.

The study, whose preliminary findings were released on Monday, was conducted by the University of Chicago’s Chapin Hall research center and Peking University. It looked at 8,900 children under age 15 from about 6,300 families nationwide.

Chen Lijun, a senior researcher at Chapin Hall, who led the study, said the children will be tracked for 20 years to identify long-term patterns.

The results were from the baseline study conducted in 2010.

In rural communities, 30 percent of the children lived with one or no parent at home, compared with 18 percent for their urban counterparts, the study found.

Nearly 25 percent of rural children were from families whose incomes were below the poverty line of 2,300 yuan ($354) annually per capita. Urban children were better off, with only 9 percent in poverty.

"A significant gap exists between the rural and urban children in many aspects ranging from their economic situation to psychological well-being, which needs to be addressed," Chen said.

Left-behind children with no parents by their side and those living in a single-parent family or with no parent are most vulnerable, he added.

According to the study, 57 percent of left-behind children aged 3 and younger have been sick in the past month, compared with those in intact rural families (43 percent) and intact urban families (40 percent) who were sick.

Moreover, 31 percent of children aged 10 to 15 from single-parent or no-parent families said they felt unhappy. Only about half that number of urban children (16 percent) said they were unhappy.

Chen suggested the Chinese government set up an integrated child service and protection system with resources and manpower to serve the various needs of vulnerable children and families.

According to the latest government estimates, China now has more than 60 million rural children whose parents left home for jobs in urban areas.