- Research Article
1
- 10.7916/d8tt534p
On the uniqueness of convex-ranged probabilities
- Jan 01, 2003
- Columbia Academic Commons (Columbia University)
- Massimiliano Amarante
We provide an alternative proof of a theorem of Marinacci [2] regarding the equality of two convex-ranged measures. Specifically, we show that, if P and Q are two nonatomic, countably additive probabilities on a measurable space (S,Σ), the condition [∃A∗ ∈ Σ with 0 P (B) =⇒ Q(A) ≥ Q(B)]. Moreover, either one is equivalent to P = Q. JEL Classification Number: D81 In [2], Marinacci proved the following theorem. Theorem (Marinacci [2]) Let P and Q be two finitely additive probabilities on a λ-system Σ. Suppose that P is convex-ranged and thatQ is countably additive. If ∃A∗ ∈ Σ with 0 P (B) =⇒ Q(A) ≥ Q(B). Proposition 1 below shows that this latter is equivalent to P = Q, and Proposition 2 proves the equivalence to Marinacci’s condition. Our condition is probably easier to check in applications. It is in this form, for instance, that the result about the equality of convex-ranged ∗Department of Economics, Columbia University, 1019 IAB, 420 W 118th street, NY, NY 10027. Email: ma734@columbia.edu.
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