The Investigation of Cost Variances
Managers are usually responsible for the control of the level of several process variables, such as cost, quality, rate of output, and so on. The levels of these process variables are known as the states of the system, and they may be represented by the values either of a continuous variable or by a discrete variable. It is assumed that these states can be ordered in terms of their desirability. Some processes may move only from a more desirable to a less desirable state while others may shift in either direction. These shifts may occur with or without the intervention of the manager. The control system is a plan formulated by management to indicate when intervention should take place. Three types of control systems are generally possible. The first involves no intervention by the manager until a breakdown of the process occurs. This approach is to be favored when the continued operation of the control system is less costly than the benefits to be derived from intervention. The second type of control system consists of periodic intervention by the manager for purposes of adjusting or otherwise influencing the process. The most compelling reason for this approach lies in its ease of application. The third approach bases the intervention decision on information obtained from the process. This information is typically obtained by sampling. The present paper will concentrate on this third type of control system. Several components are incorporated into any control system. First, the manager must establish the variable or variables to be controlled. He must