To be found disabled for the purpose of qualifying for Social Security Disability benefits, an applicant must have a medically determinable physical or mental impairment(s) so severe that he or she is not only unable to do his or her previous work but cannot, considering his or her age, education, and work experience, engage in any other kind of substantial gainful work which exists in the national economy. The regulations provide a sequential evaluation process for determining disability. In the fourth step of this process, consideration is given to the individual’s capacity to perform Past Relevant Work. The regulations state as follows: “Your impairment must prevent you from doing past relevant work. If we cannot make a decision based on your current work activity or on medical facts alone, and you have a severe impairment, we then review your residual functional capacity and the physical and mental demands of the work you have done in the past. If you can still do this kind of work, we will find that you are not disabled.” Past relevant work is work that has been performed within the past 15 years, that was substantial gainful activity, and that lasted long enough for you to learn to do it.