Vocational experts are frequent witnesses at Social Security hearings. The decision as to whether to have a VE is made by the Administrative Law Judge (ALJ). Some judges have a VE at almost every hearing, others rarely use a VE. The VE is trained in rehabilitation and has experience in the area of job placement. Specifically the VE is expect to know what is required, both on a mental and physical basis, for any job in the United States. During the hearing the VE is expected to testify about the claimant's past work. Then the Administrative Law Judge will question the VE by the use of hypothetical questions. "Please assume that she can stand for 2 hours, sit for a total of 6 hours, etc." Based upon the ALJ's questions the VE will respond that the claimant either could or could not do certain jobs.