What quality control chart compares two or more variables over time to determine how closely the variables may be related to one another?

A scatter diagram is a graphical tool used to display the relationship between two variables. Data is plotted as a collection of points, with the value of one variable determining the position on the horizontal axis and the value of the other variable determining the position on the vertical axis. The resulting pattern of points can indicate the type of correlation (positive, negative, or no correlation) and the strength of the relationship between the variables. This directly addresses the question's need to determine how closely variables are related.

A. Run chart: This chart tracks a single variable's performance over time to identify trends or patterns, not the relationship between two different variables.
C. Control chart: This is a specific type of run chart that monitors a single process variable over time against established control limits to determine if the process is stable.
D. Pareto diagram: This is a bar chart used to identify and prioritize problem areas or causes by frequency, applying the 80/20 principle, not to show correlation between variables.

1. Project Management Institute. (2017). A Guide to the Project Management Body of Knowledge (PMBOK® Guide) (6th ed.). Section 8.2.2.5 Data Representation. Newtown Square

PA: Project Management Institute.

Page 293: "A scatter diagram is a graph that shows the relationship between two variables. A scatter diagram can demonstrate a relationship between an independent variable... and a dependent variable..." This source explicitly defines the scatter diagram's purpose as showing the relationship between two variables.

2. Project Management Institute. (2017). The Standard for Program Management (4th ed.). Section 5.3 Program Quality Management. Newtown Square

PA: Project Management Institute.

Page 77: This standard notes that program quality management includes processes for incorporating quality policies and may utilize tools and techniques from project management

such as those for data analysis and representation found in the PMBOK® Guide.

3. The Pennsylvania State University. (n.d.). STAT 501: Regression Methods

Lesson 1: Simple Linear Regression. Eberly College of Science. Retrieved from https://online.stat.psu.edu/stat501/lesson/1

This university courseware states

"The most common way to visualize the relationship between two quantitative variables is a scatterplot." This confirms the academic definition and use of scatter diagrams (scatterplots) for relationship analysis.