Assign values to categories of values based on separate column attribute.

I have a large table of records some of which appear more frequently than others. I need a formula that will assign different values to each record depending on whether the test result is "positive" or "negative". Specifically, if a given record has ever tested positive, I want to flag it (and all its test entries) as an exclusion (e.g., records 2 and 4 in the example below). Conversely, if it has never tested positive, I want to include it and all its entries (e.g., records 1 and 3). I realize this will result in decision outcomes that are repeated for a single record, and that's okay.

Record_ID	Test Result	Decision
1	negative	include
2	negative	exclude
2	negative	exclude
2	positive	exclude
3	negative	include
3	negative	include
4	positive	exclude

Try this ...

=IF(COUNTIFS($A$2:$A$8,A2,$B$2:$B$8,"positive"),"exclude","include")

It works like a charm, thank you!