ABSTRACT
A basic assumption in constructing control charts, such as those for X , R, moving X , and moving R, is that the individual data points used are independent of one another. When data are taken in order, there is often a tendency for the observations made close together in time or space to be more alike than those taken further apart. There is often a technological reason for this serial dependence or ‘autocorrelation’ in the data. For example, physical mixing, residence time or capacitance can produce autocorrelation in continuous processes.
