1. A portable monitor for use in a market research study for monitoring travel and retail establishment visiting patterns of participants in the market research study, comprising: a wireless receiver operative to receive one or more position signals and to supply position data corresponding to the one or more position signals; storage operative to store venue of interest data representing locations of venues of interest pertinent to the market research study; a processor operative to process the position data to ascertain a current location of the portable monitor, to assess whether the portable monitor is within a predetermined proximity to at least one of the venues of interest based upon the ascertained current location of the portable monitor and the venue of interest data stored in the storage, and to generate, when the processor assesses that the portable monitor is within the predetermined proximity to said at least one of the venues of interest, a record including data representative of the respective venue of interest and time data representative of a time at which the portable monitor is within the predetermined proximity to the respective venue of interest.