To create a calculated field called Total Annual Income in Tableau, follow these steps:
1. Open your Tableau project and navigate to the worksheet where you want to create the calculated field.
2. Right-click on any blank space in the Dimensions/Measures pane on the left, and select "Create Calculated Field" from the context menu.
3. In the Calculation dialog box, enter a name for the calculated field such as "Total Annual Income".
4. Enter the calculation formula that adds the Annual Income variable and the Annual Income Joint variable. The formula should look like this: `[Annual Income] + [Annual Income Joint]`.
5. Check the data types of the Annual Income and Annual Income Joint fields to ensure they are both decimal data types. If not, you may need to convert them using Tableau's data conversion functions.
6. If the Annual Income Joint variable has null values, you can handle them using the ZN function. Modify your calculation formula as follows: `ZN([Annual Income])+ZN([Annual Income Joint])`. The ZN function replaces null values with zeros, allowing the addition to work properly.
7. Click the "OK" button to create the calculated field.
Now, you should see the Total Annual Income calculated field in your Dimensions/Measures pane. You can use this field in your visualizations and analysis as desired.