Kids who use media in unhealthy ways may have problems with relationships, conduct and other emotional symptoms, lead author of a US new study warned.

A study of the University of Michigan (UM) released recently on its website found that how children use the devices, rather than how much time they spend on them, is the strongest predictor of emotional or social problems connected with screen addiction.

The study has been published in the Psychology of Popular Media Culture, a journal of the American Psychological Association.

The study demonstrated that "there is more to it than number of hours. What matters most is whether screen use causes problems in other areas of life or has become an all-consuming activity," said lead author Sarah Domoff, an assistant professor of psychology at Central Michigan University.

Some of the warning signs include: if screen time interferes with daily activities, causes conflict for the child or in the family, or is the only activity that brings the child joy,

Though much research exists on adolescents and screen use, Domoff said that to her knowledge this is the first tool in the United States that measures screen media addiction in children aged 4-11.

She believes it will be a valuable tool for parents, clinicians and researchers.