Issue No.01 - January (1969 vol.18)
N. Deo , Jet Propulsion Laboratory California Institute of Technology
In general, when a logical element fails it can fail not only at true or false levels but at any one of infinitely many different voltage levels. Thus, strictly speaking, one should talk of probability density function, rather than discrete probabilities. When considering the simultaneous failures of several modules one has to consider the joint probability density function.
N. Deo, "Author's Reply<sup>3</sup>", IEEE Transactions on Computers, vol.18, no. 1, pp. 80, January 1969, doi:10.1109/T-C.1969.222532