There is provided a method of filtering a dataset comprising a plurality of records comprising the steps of : obtaining a first list of records being records corresponding to a first prescribed time period; obtaining a second list of records being records corresponding to a second prescribed time period being a time period prior to the first time period; comparing the first and second lists thereby to obtain a list of new entities being entities for which a record is present in the first list and not the second list; performing a filtering operation to obtain a filtered list being a list of entities in the list of new entries for which records do not exist in one or more datasets corresponding to a prescribed one or more time periods prior to the second time period. The method finds particular application in preventing sellers of their agents, such as estate agents, manipulating a market, such as a property market, or statistics associated therewith by withdrawing and relisting an item (property) for sale.