On the purpose of predictions

The latest issue of The Baffler has a marvelous and very humorous piece by Sam Kriss on the nature of political polling, and how and why pollsters have been getting so many things so wrong lately. But beyond comparing polling to divination or pointing out various examples of pollsters being hilariously or terrifyingly wrong, he also points to a more fundamental purpose behind predicting the future. This is the relevant passage, from the very end of the article:

Any statement about the future will, in a sense, always be wrong: it sits there, trembling, waiting for the annihilating arrival of the event, and there’s no way of distinguishing a true prediction from a false one until this moment of reckoning takes place. At the same time, though, statements about the future are also actions in the present: they change things, they create new possible realities, they reinforce or undo their own prophecies. The future does not lie hidden passively in the present, waiting to unfold. It has to be built.

This is what the biblical prophets knew. Their messages from the eternal were not like the pop-occultism of Nostradamus—this will happen, and then this, and then this—but intended to create change now. Unless you part from your wicked ways, they said, the Lord will judge you harshly. Spoiler alert: we have not parted from our wicked ways.

I bring this up here because it reminded me of a recent tweet by Jarrett Walker, author of the Human Transit blog (which sits in the links section on the sidebar to the right of this very blog):

I aspire to get through my career without ever making a prediction, except to predict that math, physics, and biological needs won’t change.

With all due respect to Mr. Walker (and believe me, he’s a man I have deep respect and admiration for), I disagree with his apparent aversion to prediction. It also strikes me as an odd sentiment coming from a man engaged in the field of urban planning.

Urban planners make predictions all the time. They make predictions about how many people will live in a city twenty or thirty years (or even further) down the line. They make predictions about how many jobs there will be. From those predictions, they derive other predictions: how much new development will take place, how bad the traffic will be, how much water the city will consume, the economic or environmental cost of all this new activity, the list goes on.

On the surface, all of these predictions seem to have the trappings of scientific fact. They involve data and complex algorithms fed into computer models that produce detailed charts and maps. From these graphics, we glimpse the horrors of a future where we do nothing: cities sprawl further across the landscape, traffic lines turn from green to red, lakes dry up. But at the end of the day, all of this is just guesswork. Educated guesswork, perhaps, but guesswork all the same.

Naturally, urban planners don’t like to think of it this way. After all, it’s a profession like any other, one deeply concerned with its own integrity and upholding its image in the world. The suggestion that the field is engaged in prophesy would likely be taken by many planners as an insult. These aren’t soothsayers, they’re experts. It’s not divination, it’s data.

Oftentimes, the predictions of urban planners don’t come true, or at least not entirely true. But here’s the crucial point: that’s not necessarily a bad thing. Accuracy is often a desirable trait when you’re trying to decipher what the future holds, but it’s not the real purpose behind these predictions. Instead, they’re meant to galvanize action in the present. If this is what may happen, the thinking goes, then we should take steps now to prepare for it.

Predicting the future does come with many potential pitfalls. But that’s not to say that one shouldn’t do it, but that one should be mindful of these pitfalls. The problem with today’s pollsters, as Sam Kriss alludes to in the linked article, is that they’re operating from an assumption that little will change, even though politics is always changing. In the case of 2016, this insistence that the fundamentals of the structure were more or less sound led to many people believing that their victory was certain, and it was only in defeat that their hubris became evident. (Incidentally, this is also partly the basis for my own prediction that Measure S will pass in Los Angeles today, so we’ll see how that prediction pans out very shortly.)

Urban planners, if anything, are more likely to suffer from the opposite problem: that the changes the future holds are so dramatic that they require massive intervention to address; this has led to plenty of cases of infrastructure being built that was wildly out of proportion to the actual need.

Planners are also likely to succumb to another pitfall, one that speaks to a degree of arrogance or over-optimism (or both, really; there’s no reason the two can’t go hand-in-hand) in the field: that the interventions planners make will have effects much more dramatic or far-reaching than what actually happens. On this point, I happen to have some more detailed knowledge.

I recently had an academic paper published that deals entirely with the predictions of planners. It’s a study of cost and ridership estimates made for bus rapid transit projects across the United States. The key finding I made in my analysis was that the ridership estimates–that is, how many people the transit planners thought were going to ride their bus rapid transit system–were usually wrong. But the problem isn’t that they were wrong, but that they tended to be wrong in a very specific way: most of the projects I studied predicted that they would see much more ridership than what they actually wound up getting. It’s in the trend that a problem becomes evident, and suggests that a more fundamental error is commonly occurring when these planners try to predict the future.

It’s unlikely that urban planners are going to stop trying to predict the future anytime soon. The entire field of long-range planning is built on a foundation of predictions. But we shouldn’t berate planners for making predictions, or swear off making them ourselves. To take another example, climatologists make predictions about the future based on observations they make today, but I think few reading this would suggest that they are wrong to do so.

Instead, let us recognize what predictions really are, and let us avoid imbuing them with the weight of certainty. Visions of the future always say more about how people feel about the present than about what will actually transpire. But visions are welcome all the same, for they give us something to act upon.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s