Which of the following are reasons why productivity of knowledge workers is more difficult to measure than productivity of industrial workers?
I. The quality of a knowledge worker's output cannot be determined immediately.
II. The output of a knowledge worker often contributes only indirectly to the achievement of the end-result.
III. Upgraded skills of knowledge workers due to rapid technological advances make output measurement difficult.
IV. Knowledge workers often assist other organizational units and this contribution is difficult to measure.