Six Sigma Green Belt Certification Practice Exam

What type of data is typically displayed on X-bar - R control charts?

1. Attribute data

2. Continuous data

3. Categorical data

4. Qualitative data

The correct answer is: Continuous data

X-bar and R control charts are specifically designed for monitoring the mean and variability of a process over time, which makes them suitable for continuous data. Continuous data is quantitative and can take any value within a given range, such as measurements of weight, length, or time. On an X-bar control chart, the sample mean (X-bar) of subgroups over time is plotted, while the R chart displays the range (R) of these subgroups. This allows practitioners to observe how the process is behaving regarding its central tendency and spread. When the engineer or quality control professional analyzes the data, it becomes clear how stable the process is, and any points outside of control limits can signal that corrective actions may be necessary. In contrast, attribute data refers to pass/fail or yes/no categorizations, which is typically displayed on different types of control charts, such as p-charts for proportions. Similarly, categorical data involves distinct groups with no meaningful numeric representation, while qualitative data covers non-numeric attributes and characteristics. Thus, these other types of data are not suitable for the X-bar and R control charts, reinforcing that continuous data is indeed the correct choice for this scenario.