<qa>  What is the median referral rate for a physician?Patients will be divided into 2 groups: Early referral to therapy and late referral to therapy by physician. To account for the fact that patients who are referred to physical therapy sooner may have a less severe injury we will be sub-grouping patients by physician. Patients of a physician with a median referral rate 10 weeks to therapy will be sub-grouped into Early referral to therapy and patients of a physician with a median referral time 10 weeks will be sub-grouped into Late referral to therapy. To account for possible changes in the way a particular physician treats their patients with a spondylolysis or spondylolisthesis physician referral rate will be assessed yearly and patient grouped based on that calendar year referral rate. For example if a doctor has a median referral rate of 12 weeks to therapy in 2009, but 9 weeks in 2010, their 2010 patients will be placed into the late referral to therapy while there 2010 patients will be placed into the early referral group. 