What is a scatter diagram primarily used to illustrate?

A scatter diagram is primarily used to illustrate the relationship between two variables. This type of graph displays individual data points to show how one variable is affected by another, allowing for the identification of trends, patterns, and correlations. By plotting data points for two different variables, one can visually assess whether changes in one variable may correspond to changes in another, thereby highlighting potential positive or negative relationships.

Understanding the correlation depicted in a scatter diagram can be crucial for decision-making and analysis in various fields, such as business, science, and social research. Identifying these relationships helps in hypothesizing and predicting outcomes, which is why scatter diagrams are popular tools in data analysis.

Other options, while relevant to data analysis and process mapping, do not capture the primary purpose of a scatter diagram. For instance, illustrations of process efficiency or steps in a work process are better represented through flowcharts or control charts. Frequency of data points would typically be shown in a histogram or frequency distribution, rather than in a scatter plot which focuses specifically on the relationship between paired data sets.