Do law-invariant linear functionals collapse to the mean?

Chen, Shengzhong; Gao, Niushan; Leung, Denny H.; Li, Lei

doi:10.48550/arxiv.2107.11239

“…For instance, additivity of the core may be sensible in our framework (Theorem 3) and it nicely connects to the scenario-based margin calculation used by CME. However, such a property is not desirable for traditional risk measures, as it essentially forces the risk measure to collapse to the mean; see e.g., Liebrich and Munari (2021) and Chen et al (2021) .…”

Section: Discussionmentioning

confidence: 99%

A Framework for Measures of Risk under Uncertainty

Fadina¹,

Liu²,

Wang³

2021

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A risk analyst assesses potential financial losses based on multiple sources of information.Often, the assessment does not only depend on the specification of the loss random variable, but also various economic scenarios. Motivated by this observation, we design a unified axiomatic framework for risk evaluation principles which quantifies jointly a loss random variable and a set of plausible probabilities. We call such an evaluation principle a generalized risk measure. We present a series of relevant theoretical results. The worst-case, coherent, and robust generalized risk measures are characterized via different sets of intuitive axioms. We establish the equivalence between a few natural forms of law invariance in our framework, and the technical subtlety therein reveals a sharp contrast between our framework and the traditional one. Moreover, coherence and strong law invariance are derived from a combination of other conditions, which provides additional support for coherent risk measures such as Expected Shortfall over Valueat-Risk, a relevant issue for risk management practice.

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“…We also construct an r.i. space on which a bounded law-invariant linear functional may fail to collapse to the mean and thus the space fails the AOCEA property. The thesis is based on [10,11]. iv to my Ph.D. studies.…”

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confidence: 99%

Automatic Continuities of Law-Invariant Risk Measures

Chen

2024

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<p>In this thesis, we investigate the automatic continuity properties of law-invariant risk measures on general model spaces. In Chapter 2, we study automatic order lower semi-continuity of law-invariant risk measures, which is usually termed as the Fatou property in the literature. Let X be a rearrangement-invariant space other than L∞ over a non-atomic probability space. We show that every real-valued, law-invariant, coherent risk measure automatically has the Fatou property at every random variable X ∈ X whose negative tails have vanishing norm (i.e., limn∥X1{X≤−n}∥ = 0) if and only if X satisfies the Almost Order Continuous Equidistributional Average (AOCEA) property, namely, d(CL(X), Xa) = 0 for any nonnegative random variable X ∈ X , where CL(X) is the convex hull of all random variables having the same distribution as X and Xa = { X ∈ X : limn∥X1|X|≥n∥ = 0 } . We also show that the AOCEA property is satisfied by most classical model spaces, including Orlicz spaces. In Chapter 3, we first show that on an r.i. space with the AOCEA property, every real-valued, law-invariant, coherent risk measure is automatically σ(X , X ′ )-lower semicontinuity at every random variable X ∈ X whose negative tails have vanishing norm. Here X ′ is the associated space of X . We also recover a local version of the Fenchel-Moreau Duality and apply it to establish automatic dual representations of risk measures. Finally, in Chapter 4, we apply our results to study when law-invariant bounded linear functionals automatically collapse to the mean, i.e., being scalar multiples of the expectation. We show that on every r.i. space with the AOCEA property, a bounded law-invariant linear functional collapses to the mean. We also construct an r.i. space on which a bounded law-invariant linear functional may fail to collapse to the mean and thus the space fails the AOCEA property. The thesis is based on [10, 11].</p>

show abstract

“…We also construct an r.i. space on which a bounded law-invariant linear functional may fail to collapse to the mean and thus the space fails the AOCEA property. The thesis is based on [10,11]. iv to my Ph.D. studies.…”

mentioning

confidence: 99%

Automatic Continuities of Law-Invariant Risk Measures

Chen

2024

Preprint

0

View full text Add to dashboard Cite

<p>In this thesis, we investigate the automatic continuity properties of law-invariant risk measures on general model spaces. In Chapter 2, we study automatic order lower semi-continuity of law-invariant risk measures, which is usually termed as the Fatou property in the literature. Let X be a rearrangement-invariant space other than L∞ over a non-atomic probability space. We show that every real-valued, law-invariant, coherent risk measure automatically has the Fatou property at every random variable X ∈ X whose negative tails have vanishing norm (i.e., limn∥X1{X≤−n}∥ = 0) if and only if X satisfies the Almost Order Continuous Equidistributional Average (AOCEA) property, namely, d(CL(X), Xa) = 0 for any nonnegative random variable X ∈ X , where CL(X) is the convex hull of all random variables having the same distribution as X and Xa = { X ∈ X : limn∥X1|X|≥n∥ = 0 } . We also show that the AOCEA property is satisfied by most classical model spaces, including Orlicz spaces. In Chapter 3, we first show that on an r.i. space with the AOCEA property, every real-valued, law-invariant, coherent risk measure is automatically σ(X , X ′ )-lower semicontinuity at every random variable X ∈ X whose negative tails have vanishing norm. Here X ′ is the associated space of X . We also recover a local version of the Fenchel-Moreau Duality and apply it to establish automatic dual representations of risk measures. Finally, in Chapter 4, we apply our results to study when law-invariant bounded linear functionals automatically collapse to the mean, i.e., being scalar multiples of the expectation. We show that on every r.i. space with the AOCEA property, a bounded law-invariant linear functional collapses to the mean. We also construct an r.i. space on which a bounded law-invariant linear functional may fail to collapse to the mean and thus the space fails the AOCEA property. The thesis is based on [10, 11].</p>

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Do law-invariant linear functionals collapse to the mean?

Abstract: In this note, we show that, on a wide range of rearrangement-invariant spaces, a law-invariant bounded linear functional is a scalar multiple of the expectation. We also construct a rearrangement-invariant space on which this property fails.

Cited by 3 publications

References 24 publications

A Framework for Measures of Risk under Uncertainty

A Framework for Measures of Risk under Uncertainty

Automatic Continuities of Law-Invariant Risk Measures

Automatic Continuities of Law-Invariant Risk Measures

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