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Mathematicians Explain Why Social Epidemics Spread Faster in Some Countries Than Others

Psychologists have always puzzled over why people in Sweden were slower to start smoking and slower to stop. Now a group of mathematicians have worked out why.

  • July 21, 2014

In January 1964, the U.S. Surgeon General’s Advisory Committee on Smoking and Health published a landmark report warning of the serious health effects of tobacco. It was not the first such report but it is probably the most famous because it kick-started a global campaign to reduce the levels of smoking and the deaths it causes.

In the 50 years since then, the patterns of smoking all over the world have changed dramatically. In the U.S., the numbers of smokers peaked in 1965 and have fallen precipitously since then. Similar patterns have occurred in all industrialized countries.

But here’s a curious thing. While the general pattern of smoking has been similar—an increase in numbers followed by a decrease—the rate of change has been dramatically different from one country to another. In other words, some countries adopted smoking more quickly and stopped smoking more quickly than others.

That raises an important question. How is smoking behavior transmitted through a population and why does it differ from one country to another?

Today, we get an answer thanks to the work of John Lang at the University of Waterloo in Canada and a couple of pals. These guys have gathered the largest historical data set on smoking ever compiled and study how its prevalence is correlated with the types of societies involved. Finally, they create a mathematical model of how smoking behavior is transmitted through a society.

Treating smoking like an epidemic in this way finally reveals what’s going on. They say their results can explain the rate of change of smoking in various industrialized countries. And they say the crucial difference is the level of individualism in each society.

Perhaps the most extreme difference in smoking patterns come from the U.S. and Sweden (see graphic above). In 1920, a relatively small portion of both populations smoked, less than 10 percent. In the U.S. this proportion rose dramatically to just under 40 percent of the population in 1965 and then fell to just under 20 percent in 2010.

By contrast, in Sweden the number of smokers peaked at around 30 percent in the early ’70s and then declined to around 20 percent in 2010. So the Swedes adopted smoking more slowly, peaked later, and then stopped smoking at a slower rate than people in America. And yet the Swedes had access to the same data about the dangers of smoking at more or less the same time.

One crucial difference between Swedish and American society is the level of individualism. This is essentially the emphasis on the worth of the individual as opposed to the emphasis on the interdependence of individuals: individualism versus collectivism.

This measure of society was promoted in the 1960s by Geert Hofstede, a Dutch social psychologist who developed ways to measure a set of cultural dimensions for comparing cultures. These include things like uncertainty avoidance; the strength of the social hierarchy; masculinity versus femininity and so on.

In the 1960s and 1970s, Hofstede surveyed more than 100,000 IBM employees to measure how these dimensions varied in different countries around the world. And since then, his ideas have become increasingly influential.

Hofstede found that societies in countries such as the U.S., the U.K., and Australia tend to emphasize individualism while societies in countries such as Sweden, France, and Japan place much greater emphasis on collectivism. In other words, in these countries there is greater social pressure to conform.

Psychologists have always assumed that patterns of behavior change more quickly in countries that emphasize collectivism. Once an idea has taken hold, the pressure to conform means it spreads rapidly. “It has previously been argued that social support mechanisms in collectivistic societies make it more likely that a person will stop smoking,” say Lang and co.

And conversely, in countries that emphasize individualism, patterns of behavior must change more slowly because there is less social pressure to conform.

The puzzle is that the data on smoking shows exactly the reverse. Sweden was much slower to adopt smoking and much slower to stop.

Now Lang and co think they know why. They’ve created a mathematical model that includes the effects of social pressure allowing them to simulate the way behavior spreads through societies with different levels of individualism.

The model reveals why Sweden stopped smoking more slowly. “Our model suggests that … social inertia will inhibit decisions to stop smoking more strongly in collectivistic societies than in individualistic societies,” say Lang and co.

Conversely, the social freedoms in individualistic societies allow anybody to make a decision to stop smoking more easily.

That’s an interesting result with significant implications for government health policies. It shows that differences in culture affect the dynamics of social spreading processes in a measurable way.

That will be crucial for the way that governments design strategies to help people stop smoking. “Interventions designed to discourage smoking should be tailored diferently in societies or social groups whose cultures differ in how they value individualism versus collectivism,” say Lang and co.

What’s more, smoking behavior is just one example of a socially contagious phenomenon. Lang and co’s approach should also apply to other forms of cultural transmission. In general, this kind of transmission should lead to slower change in societies that value collectivism versus individualism.

And that’s an idea that could influence everything from drugs policy to social network studies to the marketing of beef burgers.

Ref: arxiv.org/abs/1407.2188 : The Influence of Societal Individualism on a Century of Tobacco Use: Modelling the Prevalence of Smoking

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