For the first two areas (activities of daily living and social functioning), the rating is done based upon the following five-point scale; none, slight, moderate, marked, and extreme. For the third area (concentration, persistence, or pace), the following five-point scale is used: never, seldom, often, frequent, and constant. For the fourth area (deterioration or decompensation in work or work-like settings), the following four-point scale is used: never, once or twice, repeated (three or more), and continual. The last two points for each of these scales represent a degree of limitation which is incompatible with the ability to perform the work-related function.
20 C.F.R. §220.101