Tableau also gives you the ability to export data, including data related to trend models. This allows you to more deeply, and even visually, analyze the trend model itself. Let's analyze the 3rd degree polynomial trend line of the real estate price and size scatterplot without any factors. To export data related to the current view, use the menu and select Worksheet | Export | Data. The data will be exported as a Microsoft Access Database (.mdb) file and you'll be prompted where to save the file.
On the Export data to Access screen, specify an access table name and select whether you wish to export data from the entire view or the current selection. You may also specify that Tableau should connect to the data. This will generate the data source and make it available with the specified name in the current workbook:
The new data source connection will contain all of the fields that were in the original view as well as additional fields related to the trend model. This allows us to build a view like the following, using the residuals and predictions:
A scatterplot of predictions (x axis) and residuals (y axis) allows you to visually see how far each mark was from the location predicted by the trend line. It also allows you to see whether residuals are distributed evenly on either side of zero. An uneven distribution would likely indicate problems with the trend model.
You can include this new view along with the original in a dashboard to explore the trend model visually. Use the highlight button on the toolbar to highlight by the Address field:
With the highlight action defined, selecting marks in one view will allow you to see them in the other. You could extend this technique to export multiple trend models and dashboard to evaluate several trend models at the same time:
