Robust Individuals Control Chart for Exploratory Analysis

Apart from their uses in the context of statistical process control, control charts are also used as an exploratory tool in the context of exploratory data analysis. These two application situations are not similar and, as a consequence, control charting methodology should be adjusted to the exploratory context. In this article we make an inventory of the requirements for control charts that are used for exploratory analysis and we propose a procedure that meets these requirements. Robustness against assignable causes of variation appears to be important. The proposed methodology is illustrated from two real-life examples.