Which tool is used to analyze the relationship between two numerical variables?

The scatter diagram is a graphical tool specifically designed to analyze the relationship between two numerical variables. In a scatter diagram, individual data points are plotted on a two-dimensional graph, with one variable represented on the x-axis and the other on the y-axis. This visual representation allows one to easily observe patterns, trends, or correlations between the variables. For instance, if the points tend to cluster along a line, it suggests a strong relationship, whether positive or negative.

When assessing data to understand how one variable may impact another or to identify any potential correlation, the scatter diagram is particularly effective. This tool aids in visual recognition of relationships and assists in decision-making by providing insights into how changes in one variable might affect the other. In contrast, other options serve different purposes. Flowcharts are used for process mapping, check sheets are for data collection, and control charts are meant for monitoring process variability over time.