For children to be diagnosed with Major Depressive Disorder, they will have experienced depressive symptoms constantly for at least two weeks to such a degree that it interferes with their lives. In addition, at least four of the following symptoms must be present: changes in appetite, sleep disturbances, loss of energy, feelings of worthlessness or guilt, decreased ability to concentrate, and thoughts of suicide or death. Child psychiatrists typically use a variety of methods to assess childhood depression, including diagnostic interviews, self-report inventories, and biological signs. Typically, when physicians conduct diagnostic interviews with children, nonverbal communication, such as facial expressions, body posture, tone of the voice, and level of activity take on increased meaning since verbal skills are not as well developed in children compared to most adults. Many child psychiatrists also consider it important to obtain information from parents and teachers before making a diagnosis.