1. A method of measuring and analysing multiple data sources over a communications network in order to ascertain information about use of one or more resources linked to said communications network, said method comprising the steps of: obtaining a data source for a first group of one or more monitored resources, said first group being linked to said communications network; obtaining a further data source for a second group of one or more monitored resources, each of said second group and said first group linked to said communications network, when said further data source is obtained with respect to a group of monitored users, initially forming a first group of monitored users as a sample group so as to record and measure interactions of users in the sample group; and combining said data source and said further data source to form a single data source available to interested parties so as to ascertain usage information on one or more resources; processing the data source and the further data source, wherein the processing of the further data source is in relation to the interactions of the users in the sample group; and calibrating a value based on said data source and said further data source.