The ratio definition of efficiency has the form of a productivity measure. But the weights are endogenous variables and they do not function as weights in a productivity index proper. It is shown that extended Farrell measures of efficiency can all be given an interpretation as productivity...

The factor X in the RPI-X regulation aims to adjust price or revenue allowances to changes in total factor productivity and input prices. A cost Malmquist index can be applied to determine the efficient cost change (ECC). However, regulators typically do not have the necessary data on input...