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August 14, 2012

Measuring Cooperation and Defection using Shipwreck Data

In Liars and Outliers, I talk a lot about social norms and when people follow them. This research uses survival data from shipwrecks to measure it.

The authors argue that shipwrecks can actually tell us a fair bit about human behavior, since everyone stuck on a sinking ship has to do a bit of cost-benefit analysis. People will weigh their options -- which will generally involve helping others at great risk to themselves -- amidst a backdrop of social norms and, at least in case of the Titanic, direct orders from authority figures. "This cost-benefit logic is fundamental in economic models of human behavior," the authors write, suggesting that a shipwreck could provide a real-world test of ideas derived from controlled experiments.

Eight ideas, to be precise. That's how many hypotheses the authors lay out, ranging from "women have a survival advantage in shipwrecks" to "women are more likely to survive on British ships, given the UK's strong sense of gentility." They tested them using a database of ship sinkings that encompasses over 15,000 passengers and crew, and provides information on everything from age and sex to whether the passenger had a first-class ticket.

For the most part, the lessons provided by the Titanic simply don't hold. Excluding the two disasters mentioned above, crew members had a survival rate of over 60 percent, far higher than any other group analyzed. (Although they didn't consistently survive well -- in about half the wrecks, there was no statistical difference between crew and passengers). Rather than going down with the ship, captains ended up coming in second, with just under half surviving. The authors offer a number of plausible reasons for crew survival, including better fitness, a thorough knowledge of the ship that's sinking, and better training for how to handle emergencies. In any case, however, they're not clearly or consistently sacrificing themselves to save their passengers.

At the other end of the spectrum, nearly half the children on the Titanic survived, but figures for the rest of the shipwrecks were down near 15 percent. About a quarter of women survived other sinkings, but roughly three times that made it through the Titanic alive. If you exclude the Titanic, female survival was 18 percent, or about half the rate at which males came through alive.

What about social factors? Having the captain order "women and children first" did boost female survival, but only by about 10 percentage points. Most of the other ideas didn't pan out. For example, the speed of sinking, which might give the crew more time to get vulnerable passengers off first, made no difference whatsoever to female survival. Neither did the length of voyage, which might give passengers more time to get to know both the boat and each other. The fraction of passengers that were female didn't seem to make a difference either.

One social factor that did play a role was price of ticket: "there is a class gradient in survival benefitting first class passengers." Another is the being on a British ship, where (except with the Titanic), women actually had lower rates of survival.

Paper here (behind a paywall):

Abstract: Since the sinking of the Titanic, there has been a widespread belief that the social norm of “women and children first” (WCF) give women a survival advantage over men in maritime disasters, and that captains and crew members give priority to passengers. We analyze a database of 18 maritime disasters spanning three centuries, covering the fate of over 15,000 individuals of more than 30 nationalities. Our results provide a unique picture of maritime disasters. Women have a distinct survival disadvantage compared with men. Captains and crew survive at a significantly higher rate than passengers. We also find that: the captain has the power to enforce normative behavior; there seems to be no association between duration of a disaster and the impact of social norms; women fare no better when they constitute a small share of the ship’s complement; the length of the voyage before the disaster appears to have no impact on women’s relative survival rate; the sex gap in survival rates has declined since World War I; and women have a larger disadvantage in British shipwrecks. Taken together, our findings show that human behavior in life-and-death situations is best captured by the expression "every man for himself."

Tags: academic papers, cooperation, psychology of security

Posted on August 14, 2012 at 1:16 PM • 14 Comments

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