jnasr wrote...
Thanks, but this would only return the weighted average of ALL return
data for 1983. I am trying to screen for both a specific year and size
over 100. So the formula for 1983 should return 0, 1984 should return
22.5% and 1985 should return 10%.

Sorry, missed the size over 100 bit.

=SUMPRODUCT(--(A2:A6=1983),--(B2:B6100),B2:B6,C2:C6)
/MAX(1,SUMPRODUCT(--(A2:A6=1983),--(B2:B6100),B2:B6))