In my March 7, 2012, column, “An Elegantly Simple but Counterintuitive Approach to Analysis,” I suggested the necessity to formally assess the stability of the process producing any data—a step not usually taught in most academic statistics courses. This is done by plotting the data in their naturally occurring time order with the median put in as a reference line—known as a run chart.

This simple technique is more likely to stimulate appropriate initial dialogue than more complicated statistical analysis. It also shows the power of plotting samples calculated more frequently—monthly, as opposed to, say, quarterly or every six months. If volumes were high enough, weekly could even be used.

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