What is the difference between mild, moderate and severe cognitive impariment?

Deficit continuum: Cognitive impairment is assessed by various neurological and neuropsychological tests. Such impairment can be described in scores or other test values, which are sometimes also categorized as "mild, moderate, or severe." such general descriptions of impairment, of course, over-simplify the actual functioning or presentation of the individual. They do help when a quick abbreviation is needed.