1. A system for determining cardiovascular information for a patient, the system comprising: at least one computer system configured to: create a computational model of a first blood flow characteristic based on an anatomic model, the anatomical model representing at least a portion of the patient's vasculature and being based on based on patient-specific data regarding a geometry of at least the portion of the patient's vasculature; modify a probability model based on one or more of an uncertain parameter, uncertain clinical variable, or uncertain geometry; determine a range of a second blood flow characteristic within the patient's vasculature based on a confidence interval and the computational model of the first blood flow characteristic of the patient's vasculature; and calculate, based on the probability model and the determined range of the second blood flow characteristic, a sensitivity of the determined range of the second blood flow characteristic to one or more of the identified uncertain parameter, uncertain clinical variable, or uncertain geometry.