1. What is a control card?

A control card generally consists of :

• a central line, which may be a target indicated by a certificate, or an average obtained from repeated data, which may be fixed (static) or moving (dynamic);

• upper and/or lower limits for data with a high probability of occurrence (e.g. 95% of the population). They provide a framework for data dispersion and enable decisions to be taken when they are crossed.

As a general rule, a value above the monitoring limits will be considered suspect.

When it comes to control cards, there's no shortage of choice. Some cards are capable of storing previous data, detecting slow or rapid drift, or even taking into account the vagaries of everyday life. Some need statistical decision rules, others do not.

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