Author/Editor		Carson-Kalan, Polona; Yeh, Arthur B
Title		Exponentially weighted moving average (EWMA) control charts for monitoring an analytical process
Type		članek
Source		Ind Eng Chem Res
Vol. and No.		Letnik 47
Publication year		2008
Volume		str. 405-11
Language		eng
Abstract		The exponentially weighted moving average (EW MA) control chart is very effective in detecting small shills in process mean or variance, but so tar has not been well presented in the Held of analytical chemistry. The main diflerence from the Shewhart chart is that the EWMA chart combines current data with historical observations by essentially taking a weighted average with weighting factor n= of the moll current sample observations and historical observations. We show that the FWMA chart with 0.05 < w < 0.20 is more effective in detecting small shifts in mean and variance than the Shewhart chart. In addition, the EWMA chart can also he used to forecast the observation in the next period, which can help analysts take preventive actions before process departures to the out-ol-control state. Another advantage of using the EWMA chart is its good performance For observations that are not normally distributed or arc autocorrelaced.
Descriptors		CHEMISTRY, ANALYTICAL MICROCHEMISTRY QUALITY CONTROL