How can I get a data table to recognise and display "N/A"?
 

I have created a chart to compare figures for the past five years. There
are some categories that started only three years ago. As a result, there
are two years where the category is not applicable.

In the Excel spreadsheet (the source of the graph), I have written "N/A" for
these. In the graph, they are not graphed and the data table says "0".

What I would like is for the data table to read "N/A", so that it is clear
to those who read the graph that we didn't have zero participants, but that
the program was unavailable.

Is there any way to do this?

Jennifer