I will be that guy too then :) People tend to use relative change: d(GDP)/dt / GDP = d(Population)/dt / Population + d(Productivity)/dt / Productivity So the

I will be that guy too then :) People tend to use relative change: d(GDP)/dt / GDP = d(Population)/dt / Population + d(Productivity)/dt / Productivity So the relative change of GDP is still neatly separated into population growth component and productivity component.