In Power BI, what type of visual would you use to display two variables and their correlation over time?

Using a scatter plot is the most effective choice for displaying the correlation between two variables over time. A scatter plot allows users to visualize the relationship between two continuous numeric variables by plotting them along two axes. Each point on the scatter plot represents an observation, facilitating the identification of trends, patterns, and correlations.

When analyzing correlations, the positioning of the points reveals how one variable changes in relation to the other. For instance, if both variables tend to increase together, that indicates a positive correlation, while a negative correlation would appear as one variable increases as the other decreases. Scatter plots are particularly useful in time-related analyses because they can accommodate data points collected over time, thus allowing for an additional dimension of analysis when a time variable is added by ordering or color coding the points.

In contrast, bar charts and pie charts are best suited for categorical data rather than for examining relationships between two continuous variables. Bar charts display quantities or frequencies of categories, and pie charts illustrate parts of a whole. A line chart, while useful for showing trends over time for a single variable, does not provide the capabilities needed to assess the relationship between two variables directly. Therefore, when the goal is to explore correlation, a scatter plot is the optimal choice.