ABSTRACT
Statistical process control is based on a number of basic principles which apply to all processes, including batch and continuous processes of the type commonly found in the manufacture of bulk chemicals, pharmaceutical products, speciality chemicals, processed foods and metals. The principles apply also to all processes in service and public sectors and commercial activities, including forecasting, claim processing and many financial transactions. One of these principles is that within any
are due to two types of causes; common (random) or special (assignable) causes. Common causes cannot easily be identified individually but these set the limits of the ‘precision’ of a process, whilst special causes reflect specific changes which either occur or are introduced.
