A system and method for measuring or at least detecting the effect of at least implicit communication on transactions within a social group, optionally such as consumer purchases for example. The group may optionally comprise a social network, a pair, 3 or more individuals and so forth. By “implicit communication” it is meant communication for which there is no record, for example in a database. The aftereffects of such communication may optionally be determined, detected and/or measured through detection and/or measurement of influence, as described in greater detail below. For example, if a first consumer performs purchase of an item and a second consumer later purchases the same or similar item within a given time period, the two purchases may optionally be linked through influence which may in turn have optionally occurred through implicit communication. Optionally, the system and method may also measure or at least detect the effect of explicit communication, for which there is a record, for example in a database that describes the communication itself.