The use and misuse of statistical tools

When properly applied, statistical tools are an effective way for improving process quality. Although training on statistical process control (SPC) is increasing, unfortunately it is likely to find examples where the SPC implementation does not lead to any kind of process improvement. In fact, SPC implementation is not a simple and automatic task. Frequently, the blind use of these tools causes more perplexity than value. The availability of statistical software together with the pressure for ISO 9000 registration can partially explain this situation. In this paper, the basic principles of some statistical tools are clarified, and a case-study from a ferrous castings foundry is presented, describing a situation in which the traditional inference SPC tools are not recommended. Alternatively, graphical aids are applied in order to support process management decisions.