Independence with Lower and Upper Probabilities
This addresses foundational issues in uncertainty representation for researchers in probability theory and AI, but it is incremental as it builds on existing interval probability frameworks.
The paper tackles the problem of representing epistemological independence with interval probabilities, showing that such independence can only exist in degenerate cases like point probabilities or vacuous bounds for 2-monotone functions. It argues that these limitations depend on interpretation, being problematic for epistemological indeterminacy but expected for ontological indeterminacy.
It is shown that the ability of the interval probability representation to capture epistemological independence is severely limited. Two events are epistemologically independent if knowledge of the first event does not alter belief (i.e., probability bounds) about the second. However, independence in this form can only exist in a 2-monotone probability function in degenerate cases i.e., if the prior bounds are either point probabilities or entirely vacuous. Additional limitations are characterized for other classes of lower probabilities as well. It is argued that these phenomena are simply a matter of interpretation. They appear to be limitations when one interprets probability bounds as a measure of epistemological indeterminacy (i.e., uncertainty arising from a lack of knowledge), but are exactly as one would expect when probability intervals are interpreted as representations of ontological indeterminacy (indeterminacy introduced by structural approximations). The ontological interpretation is introduced and discussed.