Sumif?

On the attached, Ithe Overdue By column is the number of days that an item was overdue by.

I need to find the amount of times an item was overdue, per Estimator. If I do =SUMIF(D1:D10,D2,I1:I10) then it gives 17 (total days overdue), but I need it to give 3 (the number of times that an item was overdue for Jim).

I put =IF(I1:I10=" ","","1") in the next column, then did the same sumif formula as above for that column, but it comes up with 0.

Can anyone help?

ETA: Example starts from column D, and H is hidden.