According to the PMBOK® Guide, specifically within the Project Quality Management knowledge area, various data representation tools are used to analyze and communicate data.

Scatter Diagram: This is the specific tool used to identify the possible relationship (correlation) between two variables. It plots independent variables against dependent variables. The closer the data points are to a diagonal line, the more closely they are related. This helps project managers determine if a change in one factor might be causing a change in another.

Correlation Analysis: By using scatter diagrams, a project manager can see if a process variable is correlated with a quality defect, which is essential for root cause analysis and process improvement.

Why other options are incorrect:

B. Cause and effect diagram: Also known as a Fishbone or Ishikawa diagram, it is used to identify the main causes and sub-causes leading to an effect (problem), but it does not mathematically show the correlation between two specific data elements.

C. Histogram: This is a bar chart used to represent the frequency distribution of numerical data. It shows how often a particular value occurs but does not compare two different variables against each other.

D. Control charts: These are used to determine whether or not a process is stable or has predictable performance by tracking data over time against mean and control limits. They do not show the relationship between two different variables.