Combining Unreliable Pieces of Evidence
Frans Voorbraak

Abstract:
The paper discusses the problem of combining unreliable pieces of
evidence in a (generalized) probabilistic setting. The popular Dempster's
rule for combining evidence in Dempster­Shafer theory is criticized on two
accounts. Firstly, Dempster's rule is claimed to be invalid, and secondly,
the rule may fail to support intuitively acceptable conclusions. The rea­
son for this is that the application of Dempster's rule implicitly involves
making unrealistic assumptions.
It is conceded that it in many situations it may be unavoidable to make
some assumptions to reach conclusions that are of some practical use, but
often intuitively more acceptable assumptions than those used in Demp­
ster's rule can be argued for. We illustrate our position by discussing a
concrete example of sensor fusion in robotics. Further, an abstract for­
malization of belief states is proposed in which assumptions are explicitly
mentioned, and the processes conditioning and combining pieces of evi­
dence in the presence of assumptions are discussed.