Controlling bullwhip and inventory variability with the golden smoothing rule

A major cause of supply chain deficiencies is the bullwhip effect. Supply chain managers experience this variance amplification in both inventory levels and replenishment orders. In this paper, we analyse a major cause of the bullwhip effect, namely the classical Order-Up-To (OUT) policy and suggest a remedy (a smoothing replenishment rule). In general, dampening variability in orders may have a negative impact on customer service due to increase in inventory variance. We quantify the variance of the Net Stock (NS) levels and compute the required safety stock as a function of the smoothing required. The contribution of this paper is the analysis of the tradeoff between bullwhip and inventory variance resulting in a 'golden smoothing rule'. The golden smoothing rule refers to the fact that the values of two proportional feedback controllers are set equal to the Golden Ratio. [Received 5 September 2006; Revised 22 January 2007; Accepted 13 March 2007]