What is the main purpose of a trend line?

The primary function of a trend line is to indicate patterns and trends over time within a dataset. By plotting a trend line on a graph, you can visualize how data points relate to one another across a specified time period or sequence. This is crucial for identifying whether values are increasing, decreasing, or staying relatively stable over time, which helps in forecasting and understanding underlying correlations in the data.

When you observe a trend line, it provides insight into the direction and strength of the relationship between your variables. For instance, in a scatter plot showing sales data over months, a rising trend line suggests an increase in sales over that time period, allowing analysts to make informed decisions based on recognized patterns.

While other options mention useful functions, they are not the primary role of a trend line. Aggregating data categories or showing the average value pertains to summary statistics rather than the visual interpretation of trends. Filtering outliers represents a data cleaning effort, which does not align with the trend line's purpose to illustrate overall movement and direction in data over time.