If your delivery time targets are giving you a pain in the #*&! then you may be sitting on a Horned Gaussian and do not realise it. What is a Horned Gaussian? How do you detect one? And what causes it? To establish the diagnosis you need to gather the data from the most recent couple of hundred jobs and from it calculate the interval from receipt to delivery. Next create a tally chart with Delivery Time on the vertical axis and Counts on the horizontal axis; mark your Delivery Time Target as a horizontal line about two thirds of the way up the vertical axis; draw ten equally spaced lines between it and the X axis and five more above the Target. Finally, sort your delivery times into these “bins” and look at the profile of the histogram that results. If there is a clearly separate “hump” and “horn” and the horn is just under the target then you have confirmed the diagnosis of a Horned Gaussian. The cause is the Delivery Time Target, or more specifically its effect on your behaviour. If the Target is externally imposed and enforced using either a reward or a punishment then when the delivery time for a request approaches the Target, you will increase the priority of the request and the job leapfrogs to the front of the queue, pushing all the other jobs back. The order of the jobs is changing and in a severe case the large number of changing priorities generates a lot of extra work to check and reschedule the jobs. This extra work exacerbates the delays and makes the problem worse, the horn gets taller and sharper, and the pain gets worse. Does that sound a familiar story? So what is the treatment? Well, to decide that you need to create a graph of delivery times in time order and look at the pattern (using charting tool such as BaseLine© www.valuesystemdesign.com makes this easier and quicker). What you do depends on what the chart says to you … it is the Voice of the Process. Improvement Science is learning to understand the voice of the process.