Time-weighted control charts

A time-weighted control chart detects small shifts in a process mean.

Time-weighted control charts combine information from the current and past observations. They are more sensitive to detecting small shifts in the process mean than a Shewhart chart, but slower at detecting large shifts.

The charts only monitor the process mean; monitoring the process variability requires the use of some other technique.

• Uniformly Weighted Moving Average (UWMA) chart
  A uniformly weighted moving average (UWMA) chart is a type of control chart used to monitor small shifts in the process mean. It uses the average of a number of consecutive observations.
• Exponentially Weighted Moving Average (EWMA) chart
  An exponentially weighted moving average (EWMA) chart is a type of control chart used to monitor small shifts in the process mean. It weights observations in geometrically decreasing order so that the most recent observations contribute highly while the oldest observations contribute very little.
• CUmulative SUM (CUSUM) chart
  A cumulative sum (CUSUM) chart is a type of control chart used to monitor small shifts in the process mean. It uses the cumulative sum of deviations from a target.