How it works
ISA 600 (Revised) treats aggregation risk as one of the factors the group engagement team must consider when determining the nature and extent of work on components. The concept exists because component materiality is always set below group materiality. Even so, if every component has a misstatement just below its own component materiality threshold, those misstatements can sum to an amount that exceeds group materiality.
The reduction from group to component materiality is not formulaic. ISA 600 does not prescribe a specific percentage or discount factor. The group engagement team exercises judgment based on the number of components and the distribution of financial activity across them. A group with two components generating 85% and 15% of revenue faces a different aggregation profile than a group with twelve components each contributing 6%–10%. The first group can set component materiality closer to group materiality for the dominant component. The second needs a steeper reduction.
At the evaluation stage, ISA 450.11 requires the auditor to assess uncorrected misstatements individually and in aggregate. For group audits, this means collecting all uncorrected misstatements from component auditors and testing whether their sum approaches or exceeds group materiality.
Key Points
- Setting component materiality lower than group materiality is the primary control against aggregation risk.
- The more components a group has, the higher the aggregation risk if component materiality is not reduced accordingly.
- Aggregation risk cannot be eliminated; it can only be reduced to an acceptably low level.
- Failing to consider aggregation risk is a recurring finding in regulatory inspections of group audit files.
Aggregation risk vs component materiality
| Dimension | Aggregation risk | Component materiality |
|---|---|---|
| What it is | The risk that sub-threshold items combine into a group-level misstatement | The materiality amount applied to an individual component's audit |
| Who controls it | The group engagement team, through component materiality and procedures | The group engagement team sets it; the component auditor applies it |
| When it matters most | At completion, when evaluating aggregate uncorrected misstatements | At planning, when scoping the component audit |
| Common documentation gap | Not assessed at group level during the evaluation stage | Set without documented link to aggregation risk |
Worked example: Groupe Vaillant Industries S.A.
Client: French engineering group, FY2024, consolidated revenue €180M, IFRS reporter. Six reporting entities across France, Belgium, Poland, and Portugal.
Setting group materiality
The group engagement team sets group materiality at €900K (0.5% of consolidated revenue). The benchmark is revenue because the group's profit before tax has been volatile over the last two years, making it an unstable base.
Setting component materiality
With six active components, the team applies a 50% reduction. Component materiality is set at €450K. If no reduction were applied and all six components reported misstatements at full group materiality (€900K each), the theoretical aggregate would be €5.4M. The 50% factor reduces each component's contribution ceiling to €450K, capping the theoretical maximum at €2.7M.
Evaluating aggregate results
At completion, four of the six components report uncorrected misstatements: France €210K, Belgium €160K, Poland €120K, and Portugal €70K. Each is below component materiality of €450K. The aggregate is €560K.
The 50% reduction factor controlled aggregation risk. The aggregate uncorrected misstatement (€560K) stays below group materiality (€900K), and the file supports the conclusion.
What reviewers and practitioners get wrong
The AFM's inspection findings on group audits have repeatedly flagged insufficient documentation of how component materiality was set relative to aggregation risk. Teams record the component materiality figure but do not explain why that specific reduction was appropriate given the number and profile of components. ISA 600 requires the rationale, not just the number.
A second recurring issue is evaluating uncorrected misstatements at the component level in isolation without performing the group-level aggregation assessment required by ISA 450.11. A component auditor who reports "no uncorrected misstatements above component materiality" has answered a different question from "what is this component's contribution to aggregate group exposure." The group engagement team must aggregate across all components before concluding.
Key standard references
- ISA 600 (Revised) paragraphs 30–32: Requirements for setting component materiality and considering aggregation risk.
- ISA 450.11: Evaluation of uncorrected misstatements individually and in aggregate.
Related terms
Related reading
Frequently asked questions
Can aggregation risk be eliminated?
No. Aggregation risk can only be reduced to an acceptably low level. The primary control is setting component materiality below group materiality, but even with a steep reduction, the theoretical possibility of sub-threshold misstatements combining above group materiality always exists.
How do you determine the right reduction from group to component materiality?
ISA 600 does not prescribe a specific percentage. The group engagement team exercises judgment based on the number of components and the distribution of financial activity across them. A group with two components needs a smaller reduction than a group with twelve. The file must document why the chosen reduction is appropriate.