Statistics Toolbox

EWMA Charts

The exponentially-weighted moving average (EWMA) chart is another chart for monitoring the process average. It operates on slightly different assumptions than the Xbar chart. The mathematical model behind the Xbar chart posits that the process mean is actually constant over time and any variation in individual measurements is due entirely to chance.

The EWMA model is a little looser. Here we assume that the mean may be varying in time. Here is an EWMA chart of our runout example. Compare this with the plot in Xbar Charts.

• ewmaplot(runout,0.5,0.01,spec)
  
  
  

S Charts

Capability Studies