20 C.F.R. § 404.1569
The Dictionary of Occupational Titles includes information about jobs (classified by their exertional and skill requirements) that exist in the national economy. Appendix 2 provides rules using this data reflecting major functional and vocational patterns. We apply these rules in cases where a person is not doing substantial gainful activity and is prevented by a severe medically determinable impairment from doing vocationally relevant past work. (See§ 404.1520(h) for an exception to this rule.) The rules in appendix 2 do not cover all possible variations of factors. Also, as we explain in § 200.00 of appendix 2, we do not apply these rules if one of the findings of fact about the person's vocational factors and residual functional capacity is not the same as the corresponding criterion of a rule. In these instances, we give full consideration to all relevant facts in accordance with the definitions and discussions under vocational considerations. However, if the findings of fact made about all factors are the same as the rule, we use that rule to decide whether a person is disabled.
20 C.F.R. §404.1569