When a person has problems remembering things, learning new things, concentrating, or making decisions that influence their daily lives, they are said to have cognitive impairment. Mild to severe cognitive impairment occurs. People with moderate cognitive impairment may perceive changes in their cognitive skills but continue to be able to carry out their daily activities. There is no single disease or condition that causes cognitive impairment, and it is not limited to a specific age group. Cognitive impairment can be caused by Alzheimer's disease and other dementias, as well as conditions including stroke, traumatic brain injury, and developmental difficulties. It is expensive to have a cognitive impairment. People with cognitive impairment are admitted to the hospital more than three times as often as people who are admitted for another reason. In the United States, Alzheimer's disease and related dementias are projected to be the third most expensive disease to treat.