  Many extensions and modifications have been made to standard process
monitoring methods such as the exponentially weighted moving average (EWMA)
chart and the cumulative sum (CUSUM) chart. In addition, new schemes have been
proposed based on alternative weighting of past data, usually to put greater
emphasis on past data and less weight on current and recent data. In other
cases, the output of one process monitoring method, such as the EWMA statistic,
is used as the input to another method, such as the CUSUM chart. Often the
recursive formula for a control chart statistic is itself used recursively to
form a new control chart statistic. We find the use of these ad hoc methods to
be unjustified. Statistical performance comparisons justifying the use of these
methods have been either flawed by focusing only on zero-state run length
metrics or by making comparisons to an unnecessarily weak competitor.
