Which type of diagram is often used to represent relationships between variables in data analysis?

The choice of a graph as a representation of relationships between variables in data analysis is appropriate because graphs provide a visual means to convey how different variables interact with one another. In data analysis, graphs can take various forms such as scatter plots, line graphs, or bar graphs, all of which enable the analyst to observe patterns, trends, and correlations effectively.

Graphs facilitate the representation of quantitative information, allowing one to visually assess relationships (including direct, inverse, or even complex interactions) between two or more variables. For instance, a scatter plot can illustrate the correlation between variables, with each point representing a pair of values. This immediacy in displaying relationships assists in data interpretation and decision-making.

While other options such as flowcharts, tree diagrams, and bar charts serve their own unique purposes—such as illustrating processes, hierarchies, or comparisons of quantities—they do not primarily focus on illustrating the relationships between variables in the same way that graphs do. Hence, the graph emerges as the most suitable tool for this specific analytical need in data analysis.