From Lance McAlister’s blog:

Catching comparison
Hernandez: 4.99 ERA….Reds 36-30(.545) when he starts
Hannigan: 3.24 ERA…..Reds 27-15(.643) when he starts

Miller: 3.03 ERA….Reds 8-10 (.444) when he starts

I’m not making any comments…it would be more interesting broken down by starting pitcher also.