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  • Writer's pictureJerry Ratcliffe

Improving public safety by peeking at the coin

Steven Pinker is an experimental psychologist and the Johnstone Professor of Psychology at Harvard. He runs a popular general education course on rationality and generously loaded videos of his course to the net.

In one lecture, Pinker flips a coin and asks what is the probability that the coin landed on a head. The students rightly say 50 percent. But for Pinker it is 100 percent. How could the same coin and single event have a different probability for him and the audience? He glanced at it when it landed (you might argue that he cheated, but there were no rules stipulated that he could not peek).

As he says, “Probability is a function not just of the world but of your knowledge, of the information available to you.

Imagine now a lieutenant in a police department asked to come up with a strategy to combat a crime problem in her district. Generally, her choices are to (1) come up with a strategy based on her subjective experience and intuition, or (2) come up with a strategy based on her subjective experience and intuition and any additional knowledge. (see note 1)

If she is in a Compstat meeting and facing the department’s leadership, she is probably going to have to go with option 1. This is why I think Compstat, for all the accountability gains, can be harmful to good decision-making. But if option 2 is available, there are several places where additional knowledge exists. She might consult the five websites I currently recommend, and mentioned in Chapter 10 of my book Reducing Crime: A Companion for Police Leaders (you can see the five sites under ‘where to find evidence’ here). see note 2.

One common approach is to subdivide programs and practices into ‘no effects’, ‘promising’ or ‘effective’. The National Institute of Justice’s Crime Solutions website does this, and the UK College of Policing does something similar. Of course, our lieutenant will improve her likelihood of a positive outcome if she looks at the effective strategies. My point here, though, is that even trying and testing promising practices and programs will increase her knowledge.

They may not get her strategy to 100 percent, but no strategy will. This may be why astrophysicist Neil DeGrasse Tyson once tweeted “In science, when human behavior enters the equation, things go nonlinear. That's why Physics is easy and Sociology is hard.” (we could replace sociology with crime science, criminology, human psychology or just about any other ology)

When our lieutenant relies on her intuition, she is only using her subjective personal experience. However well intentioned, it is still based on a study with a single subject. Her. A researcher would say, the number of subjects in this study is n=1. When she complements her experience with the existing research evidence, she enhances her experience with the experiences of hundreds or thousands of other officers who worked on the research studies. Her n increases dramatically, and along with it, her knowledge. And knowledge can increase the probability of success, as Pinker pointed out with his coin toss example.

The evidence from numerous failed strategies has shown that crime is resilient to good intentions. If we want to improve our chances of safer communities, then we need to spend more time peeking at the coin.


(1) I know this is the basis of Bayesian thinking, but I am trying to keep this non-technical.

(2)There are many other excellent sites; however, five seemed a sensible limit. Please don’t @ me if yours was not listed.

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