"According to the traditional manufacturing-related productivity concept, productivity is defined as the ratio between outputs produced and inputs used, given that the quality of the outputs is kept constant (the constant quality assumption), or
Only if the quality of the production output is constant and there is no significant variation in the ratio between inputs used and outputs produced with these inputs, productivity can be measured with traditional methods. The constant quality assumption is normally taken for granted and not explicitly expressed. Therefore, the critical importance of this assumption is easily forgotten. [Moi ici: Forgotten por todos este pormaior fundamental. Subir na escala de valor é uma forma de dinamitar a constant quality assumption. É ela que gera o fenómeno da perseguição entre gato e o rato (salário e produtividade)] However, in most service processes it does not apply.
In services, it is not only the inputs that are difficult to calculate, it is also difficult to get a useful measurement of the outputs. Output measured as volumes is useful only if customers are willing to buy this output. In manufacturing, where the constant quality assumption applies, customers can be expected to buy an output produced with an altered input or resource structure. However, in services we do not know whether customers indeed will purchase the output produced with a different input structure or not. It depends on the effects of the new resources or inputs used on perceived process-related and outcome-related quality. Hence, productivity cannot be understood without taking into account the interrelationship between the use of inputs or production resources and the perceived quality of the output produced with these resources. The interrelationship between internal efficiency and external efficiency is crucial for understanding and managing service productivity."