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Narrative explanationin agent-based modelling   James D.A. Millington*      David O’Sullivan     George L.W. Perry        ...
When ABM are worth it   ABM most appropriate for systems with:       Interactions (between agents)       Heterogeneity ...
‘Generative’ Simulation   Specification of micro-level properties, or    rules of element interactions, used to    genera...
Statistical Portraits                         Artificial Anasazi                        Axtell et al. (2002)Statistical Po...
Elaborate Black-Boxes?“There are some warning signs here in the ABMenterprise insofar as that greatest criterion of‘succes...
ABM are Event-Driven   Event: any interaction between modelled    entities that results in a change in state of    at lea...
ABM are Event-Driven   Event: any interaction between modelled    entities that results in a change in state   Events ar...
ABM are Event-Driven   Event: any interaction between modelled    entities that results in a change in state   Events ar...
Narrative Explanation   Explain causes of events from numerous,    and potentially distal sources through a    coherent s...
What is a narrative?   NarrativeUnderstanding     Events                       http://landscapemodelling.net
What is a narrative?   Narrative      …may move back and forth between      accounts of low-level events and      system l...
An example   Breeding synchrony in bird colonies       Jovanni and Grimm (2008) Proc. R. Soc. B                         ...
An example   Breeding synchrony in bird colonies       Jovanni and Grimm (2008) Proc. R. Soc. B                 Hypothes...
Breeding Synchrony Model    SLt+1 = [(1-NR) × SLt] + (NR × NSLt) – SD   SL: stress level [initially 100-300]   NSL: neig...
Stress Level Change         NR = 0.0     NR = 0.2                        http://landscapemodelling.net
Synchrony for different NR                       http://landscapemodelling.net
Heterogeneity in context   All parameters apply to all birds identically       Only difference is initial stress level ...
Longest time to lay                      http://landscapemodelling.net
Influencing Neighbours (IN)      IN = 8           IN = 1                        http://landscapemodelling.net
Influencing Neighbours (IN)      IN = 8           IN = 1                        http://landscapemodelling.net
Reciprocal Influences                        http://landscapemodelling.net
Communication                http://landscapemodelling.net
Potential Issues   (Re)Introducing uncertainty?       From formal model to informal language       Which narrative do w...
Summary   Why simulate individuals and then report    aggregated patterns alone?       Spatially-explicit model without ...
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Narrative Explanation in Agent-Based Modelling - Millington AAG 2013

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Presentation given at Association of American Geographers Annual Conference 2013

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Narrative Explanation in Agent-Based Modelling - Millington AAG 2013

  1. 1. Narrative explanationin agent-based modelling James D.A. Millington* David O’Sullivan George L.W. Perry http://landscapemodelling.net
  2. 2. When ABM are worth it ABM most appropriate for systems with:  Interactions (between agents)  Heterogeneity (in agents’ context)  Organized Complexity (i.e., middle-numbered)Argumentthese properties mean a narratives canexplain how ABM structure producesemergent system-level patterns http://landscapemodelling.net
  3. 3. ‘Generative’ Simulation Specification of micro-level properties, or rules of element interactions, used to generate observed macro-level patterns “If you didn’t grow it, you didn’t explain its emergence” Epstein (1999, p.43) http://landscapemodelling.net
  4. 4. Statistical Portraits Artificial Anasazi Axtell et al. (2002)Statistical Portraits of Pattern http://landscapemodelling.net
  5. 5. Elaborate Black-Boxes?“There are some warning signs here in the ABMenterprise insofar as that greatest criterion of‘success’ – and the claim to novelty itself – is thatpatterns are produced as outcomes whereas theintermediate process (i.e. interactions betweensimple rules) which leads to structure is shrouded.” (Clifford 2008, p. 682). http://landscapemodelling.net
  6. 6. ABM are Event-Driven Event: any interaction between modelled entities that results in a change in state of at least one entity attribute Direction Stress Level of travel Location Wealth Any other attribute http://landscapemodelling.net
  7. 7. ABM are Event-Driven Event: any interaction between modelled entities that results in a change in state Events are consequences of code executed in context http://landscapemodelling.net
  8. 8. ABM are Event-Driven Event: any interaction between modelled entities that results in a change in state Events are consequences of code executed in context Event-driven: sequences of low-level events produce system-level patterns http://landscapemodelling.net
  9. 9. Narrative Explanation Explain causes of events from numerous, and potentially distal sources through a coherent sequence of prior events (Cleland 2011) Historical Natural Science distinguished from ‘Classical’ Experimental Science Narrative shows how a focal event or state came to occur by fitting it into a coherent account of a sequence of preceding events http://landscapemodelling.net
  10. 10. What is a narrative? NarrativeUnderstanding Events http://landscapemodelling.net
  11. 11. What is a narrative? Narrative …may move back and forth between accounts of low-level events and system level (statistical) summaries to show how they are linked … is not simply a chronicle of events http://landscapemodelling.net
  12. 12. An example Breeding synchrony in bird colonies  Jovanni and Grimm (2008) Proc. R. Soc. B http://landscapemodelling.net
  13. 13. An example Breeding synchrony in bird colonies  Jovanni and Grimm (2008) Proc. R. Soc. B Hypothesis: interactions between neighbouring birds’ stress levels drives synchrony http://landscapemodelling.net
  14. 14. Breeding Synchrony Model SLt+1 = [(1-NR) × SLt] + (NR × NSLt) – SD SL: stress level [initially 100-300] NSL: neighbour(s) stress level NR: neighbour relevance [0,1] SD: stress decay [1,100] http://landscapemodelling.net
  15. 15. Stress Level Change NR = 0.0 NR = 0.2 http://landscapemodelling.net
  16. 16. Synchrony for different NR http://landscapemodelling.net
  17. 17. Heterogeneity in context All parameters apply to all birds identically  Only difference is initial stress level Narratives more useful with heterogeneity  Heterogeneity varies context of interactions  Consequently, events are more important Modify model  so birds arrive at colony at different times  different neighbours influence stress level http://landscapemodelling.net
  18. 18. Longest time to lay http://landscapemodelling.net
  19. 19. Influencing Neighbours (IN) IN = 8 IN = 1 http://landscapemodelling.net
  20. 20. Influencing Neighbours (IN) IN = 8 IN = 1 http://landscapemodelling.net
  21. 21. Reciprocal Influences http://landscapemodelling.net
  22. 22. Communication http://landscapemodelling.net
  23. 23. Potential Issues (Re)Introducing uncertainty?  From formal model to informal language  Which narrative do we choose?  How do we know if our narrative is ‘good’ (enough)? Loss of objectivity?  Highlights subjectivities of modelling  But maybe this is a good thing… http://landscapemodelling.net
  24. 24. Summary Why simulate individuals and then report aggregated patterns alone?  Spatially-explicit model without maps Explaining ABM events via narrative can reveal process Millington et al. (2012) Geoforum james.millington@kcl.ac.uk http://landscapemodelling.net

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