Skip to content

GCRI · Mathematics, statistics and data

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.

Make an enquiry Back to Mathematics, statistics and data
01Register

Complex systems and agent-based modelling on the record.

The Global Centre for Risk and Innovation
  1. 01InstitutionThe Global Centre for Risk and Innovation (GCRI)
  2. 02The methodWhat complex systems and agent-based modelling covers
  3. 03Reference practiceComplex systems methods rely on transparent model documentation
  4. 04In systemic risk workEmergence and tipping
  5. 05Applied inPlatforms that apply this method
  6. 06StewardshipWho maintains this page
  7. 07SourcesWhere this page’s references lead
02The method

What complex systems and agent-based modelling covers.

  1. 01

    Core methods

    agent-based simulation; system dynamics modelling; nonlinear dynamics analysis; early warning indicators; emergence and pattern analysis; co-evolution modelling.

  2. 02

    Data and instruments

    micro-level behavioural data; survey and census data; observational time series; laboratory experiments; model calibration targets.

  3. 03

    Validation

    Models are evaluated by matching multiple stylised facts and patterns at different scales. Sensitivity and robustness analysis test dependence on assumptions.

  4. 04

    Limits

    Many plausible models can reproduce the same patterns. Calibration and validation data are often limited.

  5. 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.

03Reference practice

Complex systems methods rely on transparent model documentation.

ReferenceWhat it sets
ODD protocol for agent-based modelsStandard model description
IPBES Transformative Change AssessmentSystems change evidence
IRGC guidance on systemic riskGovernance of complex risks
04Process

How the process runs.

Process

Complex systems and agent-based modelling: Cascade across systems

An initial hazard can trigger later risks and events; this illustration draws one cascade across systems such as energy, water, ICT, health and transport.

  1. 01 Hazard

    1. 01Initiating hazardDataset · Competent authorityCascading risk is the risk that hazard events trigger later risks and events, through chains of interrelated hazards or impacts.

  2. 02 First-order systems

    1. 02Example system: energyModel · System operatorAn example of a system a hazard can hit first. What depends on it is set by a dependency survey.
    2. 03Example system: waterModel · System operatorA second example of a system a hazard can hit first. Its links to other systems are shown as examples only.

  3. 03 Second-order systems

    1. 04Example system: ICTModel · System operatorAn example of a system that may depend on others, for example on backup power. Survey data set the real dependencies.
    2. 05Example system: health servicesModel · System operatorAn example of a system that may depend on water, power and data. Survey data set the real dependencies.
    3. 06Example system: transportModel · System operatorAn example of a system that may depend on ICT, fuel and logistics. Survey data set the real dependencies.

  4. 04 Limiting the cascade

    1. 07Buffers and redundancyStep · Competent authorityBuffers, redundancy and restoration can limit how far an impact spreads. The OECD report moves from single assets to system resilience.
    2. 08Restoration prioritiesDecision · Competent authorityThe responsible party sets which services are restored first, under its own rules.

Outline of an external standard or method, from its public sources. It describes what the framework says, not a record of any run. It does not show that Nexus or any partner performs, certifies or approves a step. A gate is a step of the method, never a Nexus approval. The dependencies are examples. A dependency survey for the place sets them.

05In systemic risk work

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.
06Applied in

Platforms that apply this method.

07Stewardship

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.

08Sources

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.

09Questions

Questions and answers.

Why does one institution host every method page?
GCRI hosts the STEM Commons so that each method has one canonical description. Platforms link to it rather than repeat it, which keeps definitions consistent.
How do I suggest a correction to a method page?
Write to the integrity concern form with the passage and the reason.
ReportsContribute

Contribute evidence from this page.

Reports is the Consortium’s quarterly publication. What you know about this subject can become evidence, a case or a correction in the next edition, credited to you and published under CC BY 4.0 where it is your own work.

GCRI

Never send personal data, sensitive infrastructure detail or anything you have no right to share. A contribution is reviewed before use; sending it confers no authorship or editorial rights, and sponsorship never buys a finding.

The Global Centre for Risk and Innovation

Bring a method, a dataset or a question.

Information and enquiries are open today. 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.

Propose a method See all contact routes
Legal

Maps, data and figures on this site are shown for context and general information. They are not advice, forecasts or warnings; the limits of the information are set out in the Disclaimers and Data Notices.

Privacy choices