A study comparing the quality of care provided by group practices of various sizes has found that larger primary care groups outperformed smaller groups on four of six quality measures, reports The Washington Post. According to the report, published in the Annals of Internal Medicine, 73% of eligible patients in large groups received mammograms, compared with 58% of patients in smaller groups. Differences were also noted in rates of Pap smears and eye exams conducted for diabetics, but not in use of asthma medication and prescriptions for beta-blockers after heart attack. The researchers, from the University of Pittsburgh and the Harvard School of Public Health, speculate that because younger doctors are more apt to join larger practices, the difference in quality may reflect their more recent medical training.