So for example, every bug before today considered 'old', with any new bug after being 'new'. New bugs create a penalty in the metric, while the rate of reductio

So for example, every bug before today considered 'old', with any new bug after being 'new'. New bugs create a penalty in the metric, while the rate of reduction of old bugs is what's to be optimized for while not disincentivize the reporting of 'old' bugs. Hope that makes sense. I have some rough ideas, but I'd like to hope there's some battle tested formulas out there...