RP-002: Structural Model Risk — A Working Definition

Institutional publication. Not peer-reviewed.

Abstract¶

This paper formalizes a working definition of structural model risk as a distinct risk category, separate from forecast risk, market risk, credit risk, and operational risk. It extends definitional content already established in the Knowledge Centre's educational literature into a standalone, academic-register treatment.

1. Working Definition¶

Structural model risk is the risk that a financial model produces an incorrect or misleading result because of an error in its own construction, logic, or formula structure — independent of whether the business case or assumptions the model evaluates are themselves sound.

This definition isolates the model as the object of risk, separate from the decision the model supports.

2. Distinguishing Structural Model Risk from Adjacent Categories¶

From forecast risk. Forecast risk is the risk that an assumption fed into a model — a growth rate, a discount rate, a volume projection — proves incorrect once the future actually arrives. Structural model risk is orthogonal to this: it concerns whether the model correctly implements whatever assumption it is given, not whether that assumption is itself a good prediction.

From market and credit risk. Market and credit risk concern the underlying economic exposure a decision carries. Structural model risk concerns the reliability of the tool used to evaluate that exposure, independent of the exposure's own magnitude.

From operational risk in the general sense. Structural model risk is a specific instance of operational risk — the risk arising from a process or system failure rather than from market movement — narrowed here specifically to the mechanical correctness of a financial model's own construction.

3. Independence from Economic Merit¶

A central property of this definition is that structural soundness and economic soundness are independent axes. A model can be structurally flawless — every formula calculates exactly what it claims to — and still rest on an assumption a reasonable analyst would reject. Conversely, a structurally unsound model (an internally inconsistent formula, a silently excluded line item) can still produce an output that looks reasonable, purely by chance, obscuring the underlying defect. This independence is precisely why structural audit and model validation are distinct, complementary disciplines rather than substitutes for one another.

4. Structural Model Risk as the Target of Deterministic Audit¶

This definition is not merely descriptive — it specifies exactly what a deterministic structural audit engine is designed to test for. FMAE's Rule Taxonomy and its 26 individual rules, published in full in the Rule Reference, each target a specific, nameable failure mode within this risk category — a hardcoded value, a broken reference, an inconsistent formula, a silently excluded aggregation row — rather than any question about whether the model's underlying assumptions are wise.

5. Scope Note¶

This paper addresses structural model risk specifically as it applies to Excel-based financial models used in transaction evaluation, lending, and investment decisions. It does not extend or restate the separate, substantial regulatory literature on statistical and regulatory capital models used inside banks, which addresses a related but distinct problem.

Related Reading¶

• FMAE Rule Taxonomy — the operational classification of structural model risk this definition underlies.
• FMAE Scoring Engine — SM-2.0 Methodology — how structural model risk, once detected, is quantified into a single score.