bash script to count responses containing error text

I need to request a page n times and count the number of error-pages returned

ITERATIONS=100000
COUNTER=0; 
COUNT_ERROR=0; 
COUNT_EXPECTED=0; 
while (( $COUNTER < $ITERATIONS )); do 
COUNTER=$((COUNTER + 1)); 
curl http://ift.tt/1NiKrMD | grep -cim1 error; 
if (( $? == 0 )); then 
COUNT_ERROR=$((COUNT_ERROR + 1)) 
else 
COUNT_EXPECTED=$((COUNT_EXPECTED + 1))
fi; 
sleep 0.1; 
done; 
echo COUNT_ERROR=$COUNT_ERROR COUNT_EXPECTED=$COUNT_EXPECTED

This script is returning

COUNT_ERROR=0 COUNT_EXPECTED=0

... so the if clause is not executing as expected