1. A method for determining buffer inventory size: comprising: (a) selecting an item for which demand data is to be reviewed; (b) collecting demand data from a data source that relates to the selected item; (c) processing the demand data with a processing resource to determine the longest period of time to complete a requisition; (d) determining an optimum TRR that is sufficient to allow a predetermined percentage of requisitions to be completed; (e) generating a representation of dispersion of replenishment time TRR for the selected item and indicating in the representation the determined optimum TRR; (f) processing the demand data with a processing resource to determine the date of the oldest requisition for the selected item and designating this determined date as the initial starting point; (g) defining a predetermined time window equal to the optimum TRR; (h) processing the demand data within the predetermined time window starting from the initial starting point to determine the accumulated demand for the selected item during that particular predetermined time window; (i) storing the determined accumulated demand; (j) incrementing the initial starting point to provide an updated starting point; (k) processing the demand data within the predetermined time window starting from the updated starting point to determine the accumulated demand for the selected item during that particular predetermined time window; (l) storing the determined accumulated demand; (m) repeating steps (j), (k) and (l) until the end of the demand data has been reached; (n) processing all stored determined accumulated demands to determine the numerically highest accumulated demand; (o) generating a representation of the demand pattern for the selected item based on the series of determined accumulated demands determined in steps (h)-(m); and (p) setting a buffer inventory size to have a value equal to the determined numerically highest accumulated demand value.