Overall, osteopathic medical schools have more modest research programs compared to MD schools, and fewer DO schools are part of universities that own a hospital. Osteopathic medical schools tend to have a stronger focus on primary care medicine than MD schools. DO schools have developed various strategies to encourage their graduates to pursue primary care, such as offering accelerated 3-year programs for primary care, focusing clinical education in community health centers, and selecting rural or under-served urban areas for the location of new campuses. Many authors note the most obvious difference between the curricula of DO and MD schools is osteopathic manipulative medicine (OMM), a form of hands-on care used to diagnose, treat and prevent illness or injury and is taught only at DO schools. As of 2006, the average osteopathic medical student spent almost 8 weeks on clerkships for OMM during their third and fourth years. The National Institute of Health's National Center for Complementary and Integrative Health states that overall, studies have shown that spinal manipulation can provide mild-to-moderate relief from low-back pain and appears to be as effective as conventional medical treatments. In 2007 guidelines, the American College of Physicians and the American Pain Society include spinal manipulation as one of several treatment options for practitioners to consider using when pain does not improve with self-care. Spinal manipulation is generally a safe treatment for low-back pain. Serious complications are very rare. A 2001 survey of DOs found that more than 50% of the respondents used OMT (osteopathic manipulative treatment) on less than 5% of their patients. The survey was the latest indication that DOs have become more like MD physicians in all respects: fewer perform OMT, more prescribe drugs, and many perform surgery as a first option. One area which has been implicated, but not been formally studied regarding the decline in OMT usage among DOs in practice, is the role of reimbursement changes. Only in the last several years could a DO charge for both an office visit (Evaluation & Management services) and use a procedure (CPT) code when performing OMT; previously, it was bundled. The use of standardized exams as indicators of performance or aptitude has been debated. However, while less than the difference between other factors such as race (that may differ on the MCAT by 9 points or more ), there is a statistical difference of about 5 points on average MCAT scores of those who matriculate at DO schools versus those who matriculate at MD schools. There is also a difference of .16 GPA between MD and DO matriculants.