e United States has the highest gross domestic product (GDP) in the world and spends a higher proportion of its GDP on health care than any other country in the world, with little evidence to suggest that the level of public health is better than other developed countries. oped the method of small area analysis in which variations in practice patterns, spending, and outcomes could be compared across hospital referral regions. ey showed markedly dier­ent rates of hospital use between Boston, Massachusetts, and New Haven, Connecticut, for conditions without dened treatment protocols such as back pain, with no discernible dierences in outcomes.5 Using the technique of small area analysis, Fisher and colleagues between Medicare expenditures and outcomes in hospital referral regions across the United States, and found no rela­tionship between the level of health care spending and out­comes. e substantial geographic variation in rates of lumbar surgery in the Medicare population was documented by Weinstein and colleagues (Fig. 10.1).8 ese studies have shown that practice patterns vary substantially across dierent

e goal of any outcomes research study is to measure results from a study sample and extrapolate those results to under­stand health outcomes in the real world. e results of research studies are highly dependent on the details of study design,

Attrition bias results when patients drop out of a study in a nonrandom manner that is associated with the group assign­ment. If patients who failed nonoperative treatment dropped out of the study to receive surgical treatment elsewhere, the outcomes for the nonoperative patients remaining in the study would be spuriously inated. Bias in outcome detection can

RCTs can have substantial limitations and disadvantages. ey tend to be prospective studies with large sample sizes, and can be very expensive and time-consuming to perform. By design, they usually address only one primary research question. e generalizability of the study can be limited if the patients who are willing to be randomly assigned are markedly dierent from the target population. e eects of potentially harmful exposures cannot easily be studied ethically using an experimental design, although some trials involving cessation of exposures presumed to be harmful may be possible. Studies of certain interventions, especially surgery, are dicult to blind, and RCTs that are not blinded are subject to observer, detection, and performance biases. Prospective trials in which denitive treatment is not performed at the time of random­ization are potentially subject to crossover between treatment groups.