Instinctively, we feel that a system that keeps patients waiting is efficient because it keeps staff busy. However, the unseen and unused capacity results in a persistent waiting list with all its attendant risks and non-value-adding management costs.

Instinctively, we feel that a system that keeps patients waiting is efficient because it keeps staff busy. However, the unseen and unused capacity results in a persistent waiting list with all its attendant risks and non-value-adding management costs.

In spite of a massive increase in resources, waiting lists remain an inglorious attribute of the NHS. One reason is that average demand exceeds average capacity, leading to an increase in the number of patients waiting to be seen. However, in most cases, the waiting lists can remain relatively constant if we plot the total number of patients waiting each week at a particular point in a service pathway.

Queues are more likely to occur when average demand and capacity are equal but there is a mismatch between variations in demand and capacity. Demand for a service varies - patients arrive with a different case-mix every day. NHS capacity also tends to differ throughout the week.

At any point when demand is greater than capacity, excess patients have to be stored to be worked on at a later time (queue) or date (waiting list). When capacity is greater than demand, staff will be unoccupied or they will work on the queue.

A system that keeps patients waiting is efficient because it keeps staff busy. However, the unseen and unused capacity results in a persistent waiting list with all its attendant risks and -non-value-adding management costs.

Our response to prolonged waiting times is to prioritise them and reserve slots for the most vulnerable. This makes the mismatch worse as unfilled slots reserved for urgent patients can only be filled at very short notice. Inevitably resources have to be spent on forced booking, overtime, waiting-list initiatives that tend to tire staff or purchasing short-term capacity from the private sector.

So what would give better value? Ensuring that there is a little more capacity than the average demand to prevent waiting lists from building up and accepting a little slack in the system? Or by spending resources on non-value-adding waiting list managers and then more effort and time paying for inevitable end-of-year waiting list initiatives?

Not only do clinicians incorrectly believe that patients choose to fall ill just to keep any slack capacity busy but NHS managers believe that the only efficient system is one where the capacity is 100 per cent used.

Yet for hundreds of years manufacturers have shown that 100 per cent use of capacity without a queue is only possible if there is no mismatch between the variations in the demand and variations in the capacity.

So the answer to having an efficient system is to eliminate the mismatch between the variations in demand and the variations in capacity. For this, we need to demonstrate and understand it.

Not only does the NHS habit of planning based on averages guarantee that NHS resources are wasted on managing waiting lists but averages also hide the very problem we need to address - the variation.

Dr Kate Silvester is national coach for the Osprey programme, which offers clinicians an opportunity to learn and apply manufacturing systems and engineering techniques to improve timeliness, cost, efficiency and quality.