G. R. Herd’s scientific contributions

The aim of this paper is to propose certain concepts and definitions as aids in studies of the reliability of various products. ``Reliability'' and other terms commonly used in such studies are so defined that they can be measured and expressed quantitatively; and the theoretical relationship of components to the system is discussed. Reliability is studied in terms of discrete variables and continuous variables and their combined effects, with consideration of the interdependence of components The concept of dependence is developed to facilitate measurement of the effectiveness with which components are incorporated into a system. The paper advances an alternate definition of ``satisfactory performance'' to the generally accepted one based on current specification practices. The new definition takes into account user acceptance or rejection of the product. Weighting functions are proposed to give mathematical expression to user opinion versus equipment performance characteristics.