A study involving millions of people to see who they would save in the classic trolley problem has thrown up some interesting results – with dogs being the worst off.

Led by the Massachusetts Institute of Technology (MIT), the study published in Nature involved volunteers playing out various scenarios online using the “Moral Machine” experiment. In total there were 40 million inputs from 233 countries and territories over four years.

In the traditional trolley problem, participants are asked if they would cause a train – or trolley – to swerve and save the lives of five people, but killing a single person in the process. There are many variants of this idea, too.

But in the Moral Machine experiment, researchers made things a bit more complex. Focusing on self-driving cars, they posed scenarios such as whether people thought a car with a family in it should swerve to save the lives of a criminal, dog, or cat, among other scenarios.

The results showed that people preferred to save humans over animals. Dogs were saved the least, followed by criminals and cats. And younger people were generally saved more often than older people.

There were some key differences between countries, however, perhaps due to cultural differences. Eastern countries such as Islamic or Asian nations were less likely to save young people versus old people. And southern countries in Central and South America were less likely to save humans over cats and dogs. 

For the most part, people also tended to favor saving groups of people rather than individuals. But they were also more likely to save rich people over poor people, women more than men, and thin people over fat people, noted The Register.

The goal of the study was to highlight the ethical issues facing the arrival of self-driving cars in the future. Such vehicles may be required to make ethical choices at times, with some deliberation over how they should act.

Edmond Awad, the study’s lead author, told New Scientist that he hoped the findings could inform policy decisions. But not all are convinced, with ethicist H. Peter Steeves at DePaul University in Chicago noting that saving women and children, for example, was a remnant of "patriarchal views" of society.

“What we are trying to show here is descriptive ethics: peoples’ preferences in ethical decisions,” Awad told The Verge. “But when it comes to normative ethics, which is how things should be done, that should be left to experts.”

It was also noted the study was somewhat limited in that the respondents, being volunteers on the Internet, were mostly white men in their 20s or 30s.

The results are still interesting, however. And it’s good news if you’re not a jaywalker, criminal, or dog.