"the only theoretically correct and practically relevant approach to measuring service productivity seems to be to base productivity calculations on financial measures. In principle, the correct way of measuring service productivity as a function of cost effects of internal efficiency, revenue effects of external efficiency and cost and revenue effects of capacity efficiency is, therefore, the following measure:
As a global productivity measure of the operations of a service provider, the following measure can be used:
the productivity of service processes can be measured as the ratio between revenues and costs. This is a true measurement of service productivity. If revenues increase more than costs, productivity goes up. On the other hand, if a cost reduction leads to lost revenues, but the decline in revenues is less than the cost savings that have been achieved, productivity still improves. However, this may be a less recommendable strategy because in the long run it may lead to a negative image and unfavorable word of mouth, which can have a further negative effect on revenues. Thus, cost reductions may lead to a bigger drop in revenues than the savings on the cost side. If this is the case, in the long run service productivity declines."A equação que uso há anos, talvez desde 2007.
O artigo é de 2004, descobri-o em 2011.