 Rationale for the straight leg raise test: Although the true test characteristics of the straight leg raise test are unknown, a positive ipsilateral straight leg raise is felt to be a sensitive marker for a herniated intervertebral disc. Therefore, if this test is negative, it can help rule-out the disease. To maintain a homogenous cohort, subjects were stratified based on results of the straight leg raise test. Many definitions of the straight leg raise test exist. In order to identify distinct populations, the research assistants were given a strictly-defined, conservative definition of this test: namely, the test was considered positive if a subject had ipsilateral pain shooting below the knee when either leg was raised between 30 and 70 degrees, as measured with a protractor. Contralateral pain below the knee, considered more specific for a herniated disc, was also considered a positive straight leg raising test. 