A solution to crime in Tamale? The economics of false positives in attack victims

I often fantasize about plots to confound muggers and highway robbers. (I know, this probably suggests I need to go on more dates.) One of my favorite—and less disturbing—plots involves buying a knock off designer purse, filling it with rocks, and prancing around with it at Gumani intersection after dark.  I take particular pleasure in picturing how the inevitable purse snatcher will stagger under the bag’s surprising weight, and the look of dismay on his face when he opens his hard-won prize.

This paper by Cormac Hurley of Microsoft suggests this might not be such a bad idea.  The paper models the economic decision made by an attacker, taking into account the cost of initiating an attack, the payout if successful, the total number of viable targets, and the density of viable targets among the general population.  The model shows that to make attacks economical, ability to identify a subpopulation with a high density of viable targets is key.  

The paper’s findings have important implications for how we might approach crime reduction strategies in Tamale.  Generally, one can try to deter crime by increasing the cost of engaging in it, or by reducing the benefits. 

Increasing cost: You can do this in a few ways. First, you can increase the penalty if the attacker is caught.  You can also increase the likelihood that the attacker is caught.  Either way, you increase the “expected”, or average, penalty for engaging in crime.  (The rarity of catching criminals in Tamale is the main reason I am sympathetic the high penalties imposed in vigilante justice here.) You could also do this by increasing the cost of attempting an attack regardless of penalty, say by forcing attackers to sustain injury in order to get a payout.

Reducing benefits: You can reduce the benefits of attacks by reducing the frequency with which criminals get a payout (reducing the number of viable victims), or by reducing the amount of the payout if the attack is successful.

While this may all seem obvious, the Hurley paper’s model sheds some light on the efficiency of different approaches. The model suggests that reducing the frequency with which attackers get a payout can have a much larger effect than increasing the cost of crime or reducing the amount of the payout.  For instance, in one example in the paper, if an attacker can successfully identify viable victims 99% of the time, and the ratio of the payout to cost is 100, the attacker will end up attacking 32% of viable victims. If you reduce the payout to cost ratio to 20 (you could do this by reducing the payout by 80% or by increasing costs by 400%), then the attacker will attack about 15% of viable victims. However, if you reduce the attacker’s ability to accurately identify victims from 99% to 95%, the attacker will only attack 4% of viable victims.

The challenge with crime in Tamale is that the cost of committing it is pretty low, due to lackadaisical policing, and the ease with which attackers can identify viable victims: white people out late are almost always a viable target.  Increasing police vigilance will be difficult to effect, especially without risk of repercussions such as curfews and travel warnings that might lead organizations to avoid Tamale. The good news is that a strategy we can more easily implement—decreasing the percent of Tamale expats who are out late and are actually viable victims—is likely to be a much for effective strategy anyway.

So what can you do? Make sure you are not a viable victim. Don’t carry anything that could be a payout for an attacker.  Don’t do things that make you an easy target, like get drunk or carry bags that are easy to take away.  Travel in groups, and in areas where help will come quickly.

You have probably realized that a corollary to this is that increasing the total number of people who are out late, and are not viable victims, could be a very effective strategy to deterring crime.  However, in the case of Tamale muggings, being a non-viable victim still carries risks, and I am not advocating that anyone go out at night with the goal of being a “false positive” in an attempt to reduce general crime.  But if you see me at Gumani junction with a fancy bag that looks awfully full, you’ll know what’s up.