E. Ritchie

Renewal theory forecasting for stock control

Abstract A method is described for forecasting spares demand from data on model sales. The method uses concepts borrowed from renewal theory. The scheme is particularly useful for producing a forecast of all-time future demand for a spare so that a decision may be made about the timing of the final production run.

Project compression: A method for speeding up resource constrained projects which preserve the activity schedule

Abstract When projects start to overrun, control actions are necessary. For resource constrained projects, control actions to speed up the project involve reallocating resources between activities and, if necessary, bringing in extra resources. Existing planning methods are not suitable for this purpose, even when used interactively. A heuristic method is described for speeding up resource constrained projects which preserves the activity schedule. The method is illustrated by the use of an example.

Setting stock levels for wholesaling: Performance measures and conflict of objectives between supplier and stockist

Abstract The situation considered is that where a sales outlet holds a stock of goods for sale which are topped up by regular weekly deliveries. Demand is highly variable and ranges from high to very low over the many items held in stock. An appropriate stock system to use in these circumstances is an ‘order-up-to’ policy but the problem is to set the right order-up-to levels for each item. Items which experience low demand require particular care. The mathematical model used for setting stock levels for these items has to allow for the possibility of stockouts occuring before the review time and not only in the period from review to delivery. The paper consideres various measures which are used for assessing the performance of sales outlets and the implications of these measures for setting stock levels. Some measures are shown to be very sensitive to the level of sales and also need to be used with care when making interbranch comparisons. A consideration of performance measures also brings out the potential for conflict of interest between supplier and stockist.

Aspects of an inventory control study

Abstract A case study for the design of a spare parts inventory control system is described. The main emphasis is given to the problems of applying and tailoring forecasting and inventory control theory to suit the needs of a particular problem. In the main, well established methods were used and these are not described in detail. New developments arising in the course of the study have been described elsewhere.

Lot-sizing for non-stationary demand

Abstract Lot-sizing methods are reviewed and evaluated when demand varies in a systematic fashion over time. Application to two main types of inventory system are considered; spares provisioning systems, and production systems where units are stocked for use in manufacture. An assessment is made of the suitability and relative performance of the lot-sizing techniques in the two systems.

An operational research study in a group of public libraries

Abstract A description is given of an operational research investigation carried out to assist an important and urgent decision in a group of public libraries. The emphasis in the paper is on methodology: modelling the behaviour of a special set of books so that the consequences of various alternative decisions can be explored.