Graded Relative Evidence

Abstract

Relative Evidential Supports (RES) was developed and justified several years ago as a non-numeric apparatus that allows us to compare evidential supports for alternative conclusions when making a decision. An extension, called Graded Relative Evidence (GRE), of the RES concept of pairwise balancing and trading-off of evidence is reported here which keeps its basic features of simplicity and perspicacity, but enriches its modelling fidelity by permitting very modest, and intuitive, variations in degrees of outweighing (which the essentially binary RES does not). The formal justification is very simply based on linkages to RES and to the Dempster-Shafer theory of evidence. The use of the simple extension is illustrated, and to a small degree further justified empirically, by application to a topical scientific debate, about what is called the Congo Crossover Conjecture here. This decision-making instance is chosen because of the wealth of evidence that has been accumulated on both sides of the debate, and the range of evidence strengths manifested in it. The conjecture is that the advent of Aids was in the late 1950s in the Congo, when a vaccine for polio was allegedly cultivated in the kidneys of chimpanzees, which allowed the Aids infection to cross over to humans from primates.

Weighing evidence in decision systems

“…In the method proposed here this is not yet been taken into consideration. This suggests a possible further extension (Bell, 2003) of RES to include "degrees of outweighing" which we are addressing elsewhere, but in this present study we consciously retain the spirit of RES, where simple comparisons (only) are used to reason under uncertainty, and we have conjectured that this simplification is well-justified in practice.…”

“…Hooper (2000) wrote a book The River suggesting that batches of polio vaccine may have been cultured in the cells of chimps' kidneys. In Bell (2003), this is called the "Congo Crossover Conjecture", and it is denied by the scientists who developed the vaccine in Congo.…”