the frequency of each type. Control charts show plots of samples of a product or service characteristic taken from the process over time. The control chart helps us determine whether the process is in control, which means that only random variation exists. Scatter diagrams are plots on an x-y axis used to determine the relationship between two variables. Pareto charts show the frequency and cumulative percentages of defect types arranged from most frequent to least frequent defect types. This chart demonstrates which defect types cause the majority of the quality problems or complaints. A histogram shows the frequency of each quality problem.
The Pareto chart and cause-and-effect diagram can be effectively used in combination. First, the Pareto chart is used to identify the problem(s) that cause the highest number of actual defects or complaints. Next, a common problem becomes the effect on the cause-and-effect diagram. This diagram then helps us identify causes to investigate in order to solve the problem.