Systems Modelling and Qualitative Data - Modelling on the Move

Systems Modelling and Qualitative Data Dr Mike Yearworth Reader in Engineering Systems

12th April 2013

!  Purpose •  Presenting an approach to grounding systems modelling, by… •  Describing system dynamics modelling •  Describing what I mean by qualitative data analysis – specifically grounded theory •  Bringing the two together •  Practical details – using CAQDAS and some properties of binary matrices

•  Presenting results •  Debating •  Methodology – justifying the approach using arguments of multimethodology

12th April 2013

2

!  Origins of Dynamic Complexity •  Feedback! A causes B, B causes C, … causes A •  Negative feedback (balancing) – goal seeking, control system •  Positive feedback (reinforcing) – unlimited growth until bounded by exogenous factor(s) •  Combined: patterns of +ve or –ve loop dominance, •  Exponential, goal seeking, damped oscillation, limit cycles, chaotic behaviour

•  Delays complicate behaviours e.g. in –ve feedback loops •  This is not detail complexity, system structure can be quite simple yet still produce complex dynamic behaviour

12th April 2013

3

!  What  is  System  Dynamics?  

basic Forrester construct

12th March 2013

!  System dynamics modelling elements •  Causal Loop Diagrams (CLDs) •  Used to surface mental models about the behaviour of elements (variables) of the system expressed as causal relationships and feedback loops

•  Stocks and Flows (S&F) Maps •  Describe the structure of the system in terms of flows and accumulations of things

•  System Dynamics (SD) Models •  Combined CLD+S&F which describe the dynamic behaviour of a system

•  Model boundary chart •  Endogenous/exogenous/excluded variables

•  Sub-system diagrams •  Overall architecture of a model, comprising sub-systems and flows of things between sub-systems 12th March 2013

!  System Dynamics modelling process Real World

Decisions

Information Feedback

1. Problem Articulation (Boundary Selection) 5. Policy Formulation & Evaluation

4. Testing

Strategy, Structure, Decision Rules

xxx X

2. Dynamic Hypothesis

3. Formulation

Mental Models of the Real World

STERMAN, J. D. (2000) Business dynamics : systems thinking and modeling for a complex world

12th March 2013

!  Causal Loop Diagrams (CLDs) •  Relationship between variables represented by arrows linking them •  causal relationship •  can be positive or negative + + Investment

Work Completion Rate -

Jobs

Project Completion Time

Number of Project Staff Cost of Fuel

+

Car Journeys

+

Management Complexity

12th March 2013

!  Causal Loop Diagrams – textual analysis •  “Increased government investment in SWRDA will lead to the number of jobs created in Bristol going up” •  “Raising the tax on petrol will reduce the overall number of car journeys” •  Management meeting… •  Director – “Increasing the number of project staff will improve our work completion rate and improve our project completion times.” •  Project Manager – “But increasing the number of staff in my team will make my job way more complex and probably lead to worse completion times.”

12th March 2013

!  Causal links and feedback loops + W

Z -

A

B

+ X

Y

Read as W causes Z with +ve link polarity or mathematically as (∂Z/∂W>0). If the cause increases, the effect increases above what it would otherwise have been. Read as A causes B with ,ve link polarity or mathematically as (∂B/∂A