Complex performance: the development of research criteria applicable in the real world. Paper presented at the Symposium held in Amsterdam, September 1969, sponsored by the International Ergonomics Association.

The author states the inability till now on to provide the designer with precise human factors. This has stemmed from two causes: the failure of the human factors researcher to deal with system-relevant boundary conditions in his experiments, the other lies with the designer: in important respects he has succeeded through over-design and by adding a liberal portion of the extreme adaptability of the human operator.