Using the formula format provided and ensuring I press Ctrl-Shift-Enter, I am getting an error.

My information was an example scenario - would the fact that my real data is accross spreadsheets cause the error?

Here is what I have:

=IF(AND('Worksheet1'!I39:I98="",0,IF(AND('Worksheet1'!I39:I98="DME"),1,IF(AND('Worksheet1'!I39:I98="O&M",0,0.5)))

So comparing to my example:
'Worksheet1'!I39:I98 = A1
'Worksheet2'!I2 = B1
'Worksheet3'! = C1

Another concern: for the range I39:I98, every other line will never have a value because they are used for styling purposes. Does this ruin the function?