From what I understand, this is a measure of the effect of agile on the relative improvement over time of a team. I would beg to differ that it is a measure of productivity. Productivity is value delivered over time. If team A is delivering $5/week and team B is delivering $5000/week, then knowing that team A is accelerating faster than team B isn’t terribly important, particularly if the market can’t bear to absorb $6/week of whatever team A is producing.
Measuring productivity is hard. I would love to hear from people who have tried various means to measure productivity. I measure productivity in our business, but I can do that because we are small and everything we do has a direct effect on the bottom line. Does your business run with that transparency? If not, why not?