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