Surveillance, Environmental
Eric Järpe
Encyclopedia of Environmetrics, John Wiley & Sons, 2002
The first lines
In many environmental random processes it is relevant to consider a sudden shift in a
parameter of the probability distribution of the random variables. This parameter may
be a mean level of the process or the natural variation of the variables. Suddenly the
parameter can shift to some other, commonly higher, value or to another, commonly
increasing, function in time and/or space. To prevent or mitigate the fatal consequences
such shifts could imply, it is often of utter importance to detect the change as
accurately and quickly as possible. Therefore, stopping rules which are functions of
the random process data observed are evaluated, on-line or retrospectively, in order
to indicate a systematic change. Different shift processes are mentioned. An example
with data from the Swedish Radiation Safety Authority is given.