What is the test for denying disability benefits to a plaintiff?

The Secretary's denial of benefits will be affirmed if it is based on proper legal standards and if it is supported by substantial evidence. Villa v. Heckler, 797 F.2d 794, 796 (9th Cir.1986). The claimant bears the initial burden of establishing disability by showing that a physical or mental impairment prevents her from engaging in substantial gainful activity. Id. She must prove inability to return to her former type of work and not just to her former job. Id. at 798 (emphasis in original).