Complex systems and agent-based modelling
Complex systems and agent-based modelling study systems whose behaviour emerges from interactions among many components. They help explain nonlinear dynamics, tipping points and collective behaviour. Systems Science and Modelling stewards this page for the Nexus Consortium.
- 01InstitutionThe Global Centre for Risk and Innovation (GCRI)
- 02Service levelR0: information and enquiries
- 03In briefThe short answer
- 04The methodWhat complex systems and agent-based modelling covers
- 05Reference practiceComplex systems methods rely on transparent model documentation
- 06In systemic risk workEmergence and tipping
- 07Applied inPlatforms that apply this method
GCRI · Institution · service level R0
The short answer.
Complex systems and agent-based modelling study systems whose behaviour emerges from interactions among many components. Complex systems approaches explore how interacting risks can produce sudden, systemic shifts. In the Nexus Consortium, Systems Science and Modelling stewards its canonical page, and 5 other platforms apply it, including Health Nexus and Biodiversity Nexus.
Systemic exposure in World.
Where people and networks concentrate, the exposure through which shocks travel between systems, shown for World as an example geography for this subject.
What complex systems and agent-based modelling covers.
- 01
Core methods
agent-based simulation; system dynamics modelling; nonlinear dynamics analysis; early warning indicators; emergence and pattern analysis; co-evolution modelling.
- 02
Data and instruments
micro-level behavioural data; survey and census data; observational time series; laboratory experiments; model calibration targets.
- 03
Validation
Models are evaluated by matching multiple stylised facts and patterns at different scales. Sensitivity and robustness analysis test dependence on assumptions.
- 04
Limits
Many plausible models can reproduce the same patterns. Calibration and validation data are often limited.
- 05
Use in risk decisions
Complex systems approaches explore how interacting risks can produce sudden, systemic shifts. They support stress testing of policies against emergent behaviour.
Complex systems methods rely on transparent model documentation.
| Reference | What it sets |
|---|---|
| ODD protocol for agent-based models | Standard model description |
| IPBES Transformative Change Assessment | Systems change evidence |
| IRGC guidance on systemic risk | Governance of complex risks |
Emergence and tipping.
Agent-based and system dynamics models explore how interactions produce emergent outcomes such as panics, cascades and tipping. Their value is exploratory: identifying mechanisms and conditions, not forecasting. Documentation is essential because these models have many assumptions.
- Document models with the ODD protocol.
- Use for exploration, not point prediction.
- Validate patterns, not only aggregates.
- Applications on Systems Modelling and Health Nexus.
Who maintains this page.
Systems Science and Modelling stewards complex systems and agent-based modelling: it keeps this description current and reviews how the method is applied across the platforms.
Terms used on this page.
Each term as this page uses it. Where a standard-setting body defines the term, the wording follows that body.
| Term | Definition |
|---|---|
| Agent-based model | A simulation in which many individual agents follow rules and interact, producing system-level behaviour. |
| Regime shift | A large, persistent change in a system's behaviour, such as a move from calm to crisis. |
| System dynamics | A modelling approach using stocks, flows and feedback loops to study how a system behaves over time. |
| Scenario | A plausible description of how the future may unfold under stated assumptions, not a prediction. |
Where this page's references lead.
The bodies and documents this page is read against. Status and editions change; each link goes to the issuing body.
Where this page leads across the Consortium.
- Complex systems modelling for healthGCRIApplied in Health Nexus.
- Complex systems in ecologyGCRIApplied in Biodiversity Nexus.
- Complex systems economicsGCRIApplied in Economic Development.
- Complex systems in foresightGRFApplied in Foresight Nexus.
- Complex systems and agent-based modelling for financial stabilityGRAApplied in Financial Stability.
- Complex systems methodsGCRIApplied in Systems Science and Modelling.
Questions and answers.
Why does one institution host every method page?
How do I suggest a correction to a method page?
Around GCRI.
Start with an enquiry.
The current service level is R0: information and enquiries. An enquiry receives a reference and names the next step; applications, payments, compute allocations and registrations open only when their team, terms and review capacity exist.