I'm trying to calculate the stdev of a tester's results and compare it with
other testers.
B4:B15 has the testers' names
C$4:C15 has the test results that I want to calculate the Stdev for.

If I put in =Sum(IF(B$4:B15="DM",C$4:C15,0)), I get the right sum
If I put in =STDEV(IF(B$4:B15="DM",C$4:C15,0)), I get a number that is
definitely not the Stdev

I am trying to avoid having to go and individually select each test result
for each tester because the cells will have to be updated each time a tester
enters a value.

If you could help, that would be great.

Thanks.