1. A method, in a data processing system comprising a processor and a memory, wherein the memory comprises instructions which are executed by the processor to specifically configure the processor to implement a patient care plan creation and management (PCPCM) system, for correlating patient data across multiple patient data sources, comprising:generating, by the PCPCM system of the data processing system, a patient registry, in a patient registry database, comprising a plurality of patient registry records, each patient registry record being a data structure stored in the patient registry database in association with a corresponding patient and comprising personal and medical information about the corresponding patient, wherein the personal and medical information about the corresponding patient is obtained electronically from a plurality of sources, wherein the plurality of sources are computing systems providing patient data including the personal and medical information about the corresponding patient;
compiling, by at least one of a demographic and medical data analysis engine, or a lifestyle data analysis engine, of the PCPCM system, for a patient in the patient registry, a variable list associated with an input variable of a clinical rule, in a clinical rules database, and storing the variable list in a variable list cache memory, wherein the variable list comprises a plurality of instances of different personal information and different medical information from the plurality of sources, where each instance of personal information and medical information provides evidence of a different characteristic of the corresponding patient which, when analyzed in combination with other instances in the variable list, are indicative of a value to be assigned to the input variable;
processing, by the PCPCM system of the data processing system, the clinical rule; in the clinical rules database, that references the variable, at least by evaluating a criteria for setting the value of the variable based on results of processing of the variable list associated with the variable to determine if the criteria is satisfied by the plurality of instances in the variable list; and
generating, by the PCPCM system of the data processing system, results of the processing of the clinical rule, wherein processing the clinical rule comprises:
determining, for each variable in the clinical rule, whether a variable list is stored in the variable list cache memory for the variable, and
in response to a variable list being stored in the variable list cache memory for the variable, processing a combination of entries in the variable list cache memory corresponding to the instances of personal information and medical information in the stored variable list for that variable, to determine a corresponding value for that variable which is thereafter used to process the clinical rule.