  The issue of confidence factors in Knowledge Based Systems has become
increasingly important and Dempster-Shafer (DS) theory has become increasingly
popular as a basis for these factors. This paper discusses the need for an
empirical lnterpretatlon of any theory of confidence factors applied to
Knowledge Based Systems and describes an empirical lnterpretatlon of DS theory
suggesting that the theory has been extensively misinterpreted. For the
essentially syntactic DS theory, a model is developed based on sample spaces,
the traditional semantic model of probability theory. This model is used to
show that, if belief functions are based on reasonably accurate sampling or
observation of a sample space, then the beliefs and upper probabilities as
computed according to DS theory cannot be interpreted as frequency ratios.
Since many proposed applications of DS theory use belief functions in
situations with statistically derived evidence (Wesley [1]) and seem to appeal
to statistical intuition to provide an lnterpretatlon of the results as has
Garvey [2], it may be argued that DS theory has often been misapplied.
