I mocked up an example, but I may not have got it quite right.
Please adjust the attached to more closely match your true set.
It looks like your calculation should work.
Just to make sure, are your fields all coming directly from your datasource,
or are they calculated fields?
Also, will they always have a score 3: EndOY(1617)?
Please see attached files in the Forum Thread.
That seems like it should work but the calculated field is still only giving me results for EndOY1617-EndOY1516 and in cases where there is no EndOY1516 value it is not calculating EndOY1617-BOY1617.
The vast majority have a score for EndOY(1617)
The images below show the formula I'm trying and the results in the graph - where the calculated field is the fourth column (post-pre).
I am at a loss.
It would appear that the ISNULL(EndOY1516) is not falling through.
What happens if you run it without that check and just an ELSE:
(Attempted in Sheet 2 of the attached in the Forum Thread.)
Sorry for the extra work, but would it be possible for you to just take the subset data shown in your screenshot,
put that in a datasource with the Student Name etc. removed, replaced with dummy names, then recreate your workbook and post it?
256239test3.twbx 17.4 KB