1. A method for simulating a group, comprising: providing a data storage medium having a predetermined group database entity type wherein each instance of the group database entity type includes: (a-1) an identification storage area for identifying a corresponding group of items, and (a-2) a group type storage area for identifying the corresponding group as one of: (i) an actual group of one or more items, and (ii) a simulated group of one or more items; wherein the predetermined group database entity type defines a substantially entire data organization for each instance of the group database entity type within a data repository; providing access to at least a first instance of the predetermined group database entity type using a value in the identification storage area of the first instance, wherein a value for the group type storage area identifies the first instance as corresponding to an actual group (G 1 ) of one or more items; wherein for evaluating a performance of the first instance, item performance data (ED 1 ) associated with the items of the actual group G 1 is accessed according to Type 2 constraints for accessing ED 1 , wherein the item performance data ED 1 is substantially for a time period no earlier than a creation of the actual group G 1 ; creating a second instance of the predetermined group database entity type on the data storage medium, wherein the second instance corresponds to a simulated group (G 2 ) of one or more items; wherein the step of creating includes storing a predetermined time value for determining, for the items of G 2 , an earliest date of creation for item performance data that is desired for simulating an evaluation of G 2 , wherein the predetermined time value is substantially prior to the creation of G 2 ; second evaluating a performance of the simulated group G 2 , wherein item performance data (ED 2 ) associated with the items of the simulated group G 2 is accessed for performing the second evaluation; wherein the accessing of the item performance data ED 2 is determined using the predetermined time value; wherein the predetermined group database entity type provides a common data structure for accessing substantially all data for each of the first and second instances and wherein a supervisor of the actual group G 1 is enabled to create the simulated group G 2 and wherein the simulated group G 2 created by the supervisor comprises an agent not in the actual group G 1 .