You can use reference elements and line connections to show trends over time.

In a production environment, a production or yield engineer wants to understand yield drift over time across production lines by observing whether a metric (for example, median or mean) is trending up or down. In Spotfire, they can create trend lines by using reference elements and line connections to gain these insights about their data.

In the following example, an analysis contains a data table with yield values across three production lines. The measurements are affected by gradual drift and noise.

Configure a box plot to show Date(Month) on the category axis and Yield on the value axis. Make sure that the box plot is not sorted. For more clarity, you can remove Histogram, Confidence interval (95%), and Comparison circles.

Add a Reference layer to the box plot. Remove the Line that is automatically added, add a Marker , and configure Value to be Median([Axis.Y.Column]), which refers to the median of the column that is selected on the Y-axis. If you want, adjust the marker size.

Add Labels to your markers. Adjust the vertical text alignment and the font settings for better readability.

Add a Line connection to see trends across all production lines over the year.

Add Production_Line to the category axis and apply Color by Production_Line both to the box plot and the reference layer to show trends over the year for each production line.

Add Trellis by Production_Line to only the box plot but not the reference layer. In this way it is easier to see and evaluate the trends for each production line and still be able to compare it to the trends of the other production lines. Use the manual trellis layout to only examine one production line at a time.