From the World in the Model to the Model in the World

© M.S. Morgan, 2012

From the World in the Model to the Model in the World

Mary S. MorganLSE & University of Amsterdam

BA “Modelling for Policy” Conference May 17-18th, 2012


Modelling creates ‘small worlds’: the ‘world in the model’

A. Scientists represent our world into small models B. Those ‘small worlds’ become autonomous

working objects used as means of scientific enquiry

1. We enquire into the small world in the model to help us work through our theories and hunches.

2. We use the small model world to enquire with into the big world we live in to see if the models can help us understand that world, and intervene (policy) in useful ways.


The qualities of small worlds as working objects for science?

Models are representations that create manageably small and manipulable worlds

Small does not necessarily mean simple, silly or simplistic but rather compressed or miniature worlds.

• Think maps: not every detail given but exhibit relations we cannot grasp by eye.

• Think poetry: spare, but dense, expressive prompts to imagination and understanding


The qualities of small worlds as working objects for science?

Models are representations that create manageably small and manipulable worlds

• Small does not necessarily mean simple, but rather compressed/miniature worlds.

• Manipulability: a models needs resources that can be used as means of enquiry and to suggest modes of action


Manipulable resources in models


Using small worlds as technologies of enquiry

Into the world of the model and with the model into the world the model represents

Technology = a form of experiment: questions, model manipulations, and answers

• Eg Samuelson’s algebraic model• Eg Tinbergen’s statistical model• Eg Newlyn-Phillips hydraulic model


Samuelson’s macro-economic system (1939)


Tinbergen’s economic model for the Great Depression (1939)


Newlyn-Phillips Hydraulic macro-economic model (1949)

Now in London Science Museum, computation gallery



Technology of enquiry

Working with models = a form of experiment: with questions, model manipulations, answers.

• Eg Samuelson: enquiry into world in model • Eg Tinbergen: enquiry with the model into the

world• Eg Newlyn-Phillips Machine: enquiry into the

world in the model and with the model into the world


Experiments: seek valid inference, not correspondent truth, between model and world

• Lab experiments – internal validity (within the lab) and external validity (beyond lab)

• Model experiments – internal validity (in world of model) and parallel validity (in real world)

• External and parallel validity both problematic and no easy solution to either!

• Statistical ‘experiments’ – rules for statistically valid inference within and beyond the model, but may not be sufficient for action: eg demography


So …..

• Models may be truth-makers about the small world in the model, but not of the world that the model represents

• Rather – learning about the world from working with models is best conceived as an inference problem ….

• …. which invites modest claims about how much we can learn about the world from models, and

• ...... scepticism about action in the world based on models, and the dangers of using models as “engines not cameras” (Donald Mackenzie, 2006)


With sufficient usage, models slide from being a lens to view the world into those things seen in world

Using small world accounts has imaginative and cognitive aspects that alter what we see and our ability to understand the world

• Imaginative: think poetry, we see new things in the world because expressed in new ways

• Cognitive: think tube map, and way we start to see world in terms of the map


‘Performativity’ of models follows cognitive and imaginative shift

Acting on, and with, small world models has potential to re-make the big world on the basis of the recipes found in the small worlds

• Eg economic models and addiction (eg min. pricing for alcohol in Scotland)

• Eg epidemiological models and vaccinations (eg Good-night Kiss model?)

Sometimes this makes the big world behave more like the small world in the model, sometimes less!


Model-based actions don’t always work in big world, because model

• is a misleading/insufficient representation• is good at description but does not give access to

behavioural/causal structures • gives access to plausible explanations, but not to

recipes that suggest means of action • its ceteris paribus conditions do not hold in world• suggests modes of action that are not consistent

with other actions being taken• is not updated with feedback from rapidly

changing situation in world ………………….. etc


Health Warnings 1 and 2:

1) Model-based actions may be counter-performative, even dangerous …think seriously about using model to re/make the world

2) For the scientist, danger lies where there is no distinction between the world in the model and the model in the world


Thank you

Education

From the World in the Model to the Model in the World