Comparing and combining individual x ‐charts and x ‐bar charts

Control charts have played an important role in monitoring the performance of operation processes, ever since their invention. Traditionally, according to Juran's idea and others, x ‐bar charts are more sensitive than individual x ‐charts. However, such a conclusion is valid only under certain conditions. Individual x ‐charts can outperform x ‐bar charts in some situations, especially in cases of minor and extreme changes of the center value. Since each chart has its own advantages and disadvantages, the idea of combining the results of these two charts is studied. The finding seems to be useful for practitioners in quality control.