The orders already on their way

The visible gap

Inventory is low, so a manager places an order. The next report still shows a shortage, so another order follows. Then the deliveries begin to arrive together. The warehouse fills, new orders stop, and the system may swing back toward shortage.

The missing state

Orders in transit are not yet on the shelf, but they are commitments that will change the shelf later. A decision rule that ignores that pipeline can respond repeatedly to a gap that previous actions are already addressing. The timing of delivery and reporting determines how long the gap remains misleading.

What Sterman studied

In controlled experiments with a simulated supply chain, John Sterman found that participants often failed to account adequately for the supply line. Their decisions produced amplification and oscillation. This is evidence about behavior in that task, not a claim that every supply chain problem has the same cause.

Similar curves, different causes

Lee, Padmanabhan and Whang identify additional sources of the bullwhip effect, including order batching, price variation, demand-signal processing and rationing behavior. A wavy order history is not enough to choose among these explanations. You need observations of how orders are formed.

Try changing the information

The delay lab lets you include the pipeline in the order rule. Compare stock, outstanding orders and backlog. Watch whether a change in information helps under the selected gain and delays. The simulation is a teaching model, not a calibrated inventory policy.