Why model?

I came across this little paper on the Introduction to Dynamical Systems and Chaos online course from Santa Fe. It was provided as a supplementary reading in the ‘Modelling’ section. The paper lays out some of the most enduring misconceptions about building models.

“The modeling enterprise extends as far back as Archimedes; and so does its misunderstanding.” Epstein (2008)

So, why model? What are models? And who are modellers?

Prior to reading this paper, my short answers to these questions would have been in accordance with the widely held misconceptions that:

We model to explain and or predict. Models are formal representations (often mathematical) of phenomenon or processes. And a modeller is someone who builds these explicit formal mathematical models. However, Epstein explains:

“Anyone who ventures a projection, or imagines how a social dynamic—an epidemic, war, or migration—would unfold is running some model.”

I like the idea that we all run some implicit models all the time. In the social and political sphere, where it is extremely difficult to operationalize and specify variables, this perspective gives implicit modelling such as drawing dynamical analogies, its due importance.

The paper lays out 16 reasons other than prediction for building models. And the idea that prediction and explanation aren’t the only modelling goals was revelation to me given that I’ve had a love hate relationship with modelling in the past. I am attracted to models, specially those with dynamical systems inclination but the overall tendency towards prediction as a goal often frustrates me. Just to clarify, prediction is a fine goal but my objection arise when 1) we’re deluded into thinking that models give us the tools to predict specific individual behaviours and 2) we can model a phenomenon, especially human behaviour, without first understanding it.


xkcd: Machine Learning

Let me elaborate further in the context of automated predictive system that are currently trending (at least, within my academic circle) and often preoccupy my thinking. Claims to predict “criminal” and “risky” behaviour are examples from last week’s headlines: UK police wants Artificial Intelligence (AI) to predict criminal behaviour before it happens and Predictim, a commercial data analytics firm, claims its AI can flag “risky” babysitters. Unfortunately, these are not the outrageous exceptions but the general direction where things in the digital surveillance sphere seem to be heading.

Behaviours such as “criminal” or “risky” are very complex adaptive behaviours which are a result of infinite ongoing factors, which we can never fully specify in the first place. This makes it impossible to predict criminal behaviour with certainty. Juarrero reminds us why it is impossible to predict human behaviour with precision:

“When we are dealing with complex adaptive systems, surprises are unavoidable. Because of their sensitivity to initial conditions – due, in turn, to their contextual and temporal embeddedness – complex adaptive systems are characterized by unusual twists and novel turns. Since we will never be able to specify any dynamical system’s initial conditions to the requisite (infinite) degree, a fortiori we will never be able to capture all the details and circumstances of anyone’s life and background. Given this limitation, we must always keep in mind that reconstructing specific instances of behavior will always be, at best, an interpretation and not a deduction – a much more fallible type of explanation than we had previously hoped was available. Interpretations of human action are always tentative. Absolute certainty about either what the agent just did, or what he or she will do – specifically – a year from now, is therefore impossible.” (Juarrero 1999, p. 225)

These claims to predict “criminal” or “risky” behaviour are more than a mere misunderstanding of human nature or simple illusions about what AI tools are capable of doing. As these tools are being implemented into the social world, they have grave consequences on people’s lives. When claiming to predict someone’s potential criminality, errors are inevitable. The stakes are high when we get things wrong. Unsurprisingly, it is often society’s most vulnerable, those who are disfranchised, that pay a high price. Indeed, such models are used to further punish and disfranchise those that fall prey to these models.

A slightly different but interrelated issue with modelling to predict is that the strive to predict and explain often ignores the value of describing and/or observing to gain deep understanding. Sure, describing to understand, and explaining and predicting aren’t mutually exclusive. However, in reality, we seem to have blindly adopted prediction and generalization as primary goals of science. Studying to describe and understand, as a result, are undervalued. What is the point of describing? you might ask. I think it is fundamental to understand any phenomena or process as deeply and comprehensibly as possible before we can attempt to explain or predict it, and description is key to gaining such understanding.

I’ll leave you with an insightful Geertz (1973) passage from The Interpretation of Cultures:

“… I have never been impressed with claims that structural linguistics, computer engineering or some other advanced form of thought is going to enable us to understand men without knowing them.”



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