Measuring Effectiveness of NPs During the last 30 years, a large number of studies have documented the safety of NPs as effective providers of primary care. These studies compared outcomes of patients who received NP care with outcomes of patients who received physician care. One of the best designed studies, the Canadian Burlington Randomized Trial, was conducted in the early 1970s. NPs safely and effectively managed 67% of their patient visits without physician consultation, with the remaining 33% of the patients appropriately referred to physicians for management