It had become clear that the itemized changes experimentally imposed, although they could perhaps be used to account for minor differences between one period and another, yet could not be used to explain the major change - the continually increasing production. This steady increase as represented by all the contemporary records seemed to ignore the experimental changes in its upward development.
p. 65, chapter 3: The Hawthorne experiment Western Electric Company - The Human Problems of an Industrial Civilisation, (1933)