R

icher countries have higher rates of anxiety in their population than poorer countries and — in a finding that surprised even the researchers — that anxiety also interfered more with daily activities and responsibilities.

Specifically, there was a higher proportion of people in higher-income countries with generalized anxiety disorder, or GAD — defined as excessive and uncontrollable worry that affects a person’s life — and with severe GAD. The researchers, who are members of the WHO World Mental Health Survey Consortium, published their findings in JAMA Psychiatry on Wednesday.

For example, Australia and New Zealand, both identified as high-income countries, had the highest lifetime prevalence rates — 8 percent and 7.9 percent, respectively. Nigeria (0.1 percent) and Shenzhen, China (0.2 percent), had the lowest rates reported; both were categorized as low-income areas.

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Why it matters:

“We’re trying to make the case with these data that this is a disorder that is reasonably prevalent and associated with a substantial role impairment, and we need to be paying attention to it in clinical settings,” said lead author Ayelet Meron Ruscio, a psychology professor at the University of Pennsylvania. The data could also serve as a first step to understanding how GAD presents or develops in different countries, which would be useful for people developing prevention and treatment programs.

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Researchers thought prevalence rates might be different in lower-income countries because of the relative political or economic instability. These circumstances could have directly contributed to higher rates — or indirectly led to lower rates, since people might not report “excessive” anxiety because their worries were justified by the issues they faced.

But no one has actually reported about this much data in this many countries since the diagnostic criteria for GAD changed in 2013. (The consortium also published results in 2004 and 2009 about prevalence and treatment rates of some mental illnesses in over a dozen countries.)

The nitty-gritty:

Researchers analyzed data from interviews with nearly 150,000 people in 26 countries over 12 years to determine if people had GAD as defined in psychology’s key reference text, the Diagnostic and Statistical Manual of Mental Disorders. People with GAD were also asked if it had interfered with their everyday responsibilities and activities.

Countries got sorted into low-income, middle-income, and high-income categories based on gross national income per capita — a measurement based in part on gross domestic product. (It’s the same criteria the World Bank uses.)

The American Psychiatric Association published the latest version of the DSM in 2013 — after the surveys were administered — so researchers had to take the modified criteria into account when they analyzed their data. One of the biggest changes: DSM-IV didn’t allow practitioners to diagnose people with GAD if symptoms only happened when patients also had symptoms of a mood disorder like bipolar disorder or depression. The DSM-5 does.

But keep in mind:

This study may actually underestimate the prevalence of GAD. The interview tools they used tend to produce conservative estimates, the authors stated. The response rates to the surveys also varied widely by country.

There is also one obvious limitation to comparing prevalence rates across countries: Social and cultural conventions influence how likely someone is to self-report symptoms of anxiety to an interviewer and how likely those symptoms are to be recognized as clinically significant. GAD has been defined primarily on how it presents in people living in countries like the United States, Ruscio noted. (Some studies have shown that anxiety may present with more physical symptoms in non-Western countries.)

Associations between a country’s income and GAD prevalence doesn’t meant that prevalence differences within a country should be ignored. The association between lower income and higher rates of anxiety disorders within a country has been well-established, said Ruscio. These results don’t change that.

Several of the authors disclosed grants and honoraria from pharmaceutical companies; one author co-owns a health care market research firm.

What they’re saying:

Researchers who had not worked on the paper could not be reached for comment Tuesday evening or Wednesday morning. (Some of the researchers contacted lived in areas affected by winter storm Stella, the blizzard that hit the East Coast on Tuesday.)

But this paper builds on lots of other work done by the WHO’s Mental Health Survey Initiative. The initiative doesn’t just study anxiety — researchers have also collected data about substance abuse, mood, and behavioral disorders. Another study from the group that also found lower rates of mental disorders in some lower-income countries had chalked up the findings in part to methodological issues.

The bottom line:

On average, GAD is more prevalent in higher-income countries, but that doesn’t necessarily mean there are fewer anxious people in lower-income countries. Many different factors, including diagnostic criteria and social conventions, may be responsible.

Lifetime prevalence of DSM-5 anxiety:

All locations: 3.7 percent

Nigeria 0.1 percent

Shenzhen, China 0.2 percent

Poland 0.9 percent

Beijing, China and Shanghai, China 1.0 percent

Romania 1.0 percent

Peru 1.1 percent

Mexico 1.1 percent

Germany 1.5 percent

Colombia 1.9 percent

Spain 1.9 percent

Italy 2.1 percent

Bulgaria 2.3 percent

Lebanon 2.3 percent

Japan 2.6 percent

Belgium 2.8 percent

Ukraine 3.3 percent

The Netherlands 3.6 percent

South Africa 3.6 percent

Medellín, Colombia 3.8 percent

Israel 4.4 percent

Iraq 5.0 percent

Brazil 5.1 percent

Portugal 6.1 percent

France 6.2 percent

Northern Ireland 6.4 percent

Murcia, Spain 7.0 percent

United States 7.8 percent

New Zealand 7.9 percent

Australia 8.0 percent

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