To the Editor In a Viewpoint, Dr Sharfstein and colleagues assessed the state of evidence on Maryland's hospital global budget program. 1 We agree with much of their synthesis, including that hospital admissions declined in Maryland following the program's implementation, but we are not convinced that these changes can be attributed to global budgets.Because admissions also decreased in other states, it is important to select an appropriate control population to isolate changes associated with hospital global budgets. 1 The standard assumption is that differences between intervention and control populations would have remained constant without Maryland's policy and, therefore, any differential change from the preintervention to the postintervention period can be interpreted as a policy effect. Evidence of parallel preintervention trends supports this assumption but does not guarantee it holds. 2 In 2 recent studies of Maryland's program, the standard assumption was not supported because preintervention trends differed on most outcomes. 3,4 In both studies, researchers recognized this problem and made the assumption that, absent the intervention, differences in preintervention trends between Maryland and the control population would have continued into the postintervention period. Although reasonable, this assumption may be violated because differential trends are unlikely to continue indefinitely.In the study by Roberts et al, 3 this seemingly minor methodological issue was critically important. Under one assumption, Maryland's program may have been associated with changes in admissions, but the conclusion differed under the other assumption. Other issues, such as how to address the increasing use of hospital observation stays, were also important in evaluating the program.In situations in which methodological choices may affect the conclusion, it is important to conduct sensitivity analyses and to assess the totality of evidence. The sensitivity analyses in the study by Roberts et al 3 suggested that the differential reduction in admissions in Maryland was not uniquely large, and results from a separate study of Maryland's pilot introduction of global budgets in rural hospitals (where treatment and control groups had similar trends before introduction) 5 found no change in hospital utilization due to global budgets.Based on the totality of evidence, we believe caution is needed in ascribing early changes in utilization to global budgets in Maryland. The inability of researchers to confidently identify early effects of Maryland's program does not imply that this policy failed, nor does it preclude the potential for effects to emerge over time. Continued evaluation and efforts to strengthen Maryland's model, as Sharfstein and colleagues advocated, 1 remain vital next steps.