1. A system for detecting statistical variations in public opinion comprising: A Respondent Interface Subsystem for capturing respective opinion values of a set of respondents in relation to a subject matter, said respective opinion values having respective validity periods associated therewith; a Database Subsystem for storing said respective opinion values corresponding to each respondent and to said subject matter; a Statistical Processing Subsystem for calculating successive values of a Collective Opinion Value by selecting respective subsets of said respective opinion values according to said respective validity periods and calculating said successive values of a Collective Opinion Value over said corresponding subsets.