India and China have made much of the advance of the middle class in recent years. Now, Kharas said, Southeast Asian countries like Thailand and Vietnam are ready for a wave of the middle class.

4. So what does it look like and feel to be part of the global middle class all over the world?

Dollar Street, the project of the Swedish non-profit organization Gapminder, has photographed the daily lives of more than 250 families around the world. Their subjects include a family of five in Burundi, living on $ 324 a year and a family of five in China that makes $ 121,176 per year. The photos show the people and their homes, eating utensils, toilets, toothbrushes and transport, allowing people to compare lifestyles around the world.

Dollar Street recently photographed Angga and Yuli Yanvar, a couple in the early years & # 39; 30 with two young children, part of the emerging middle class in Indonesia. Angga is a social worker and Yuli is a teacher. The family has a refrigerator, electricity and an engine to be around, and their children have different toys, including bicycles and a battery-powered minicar. They save money to buy a house and car, goals that seem realistic in view of the fact that they earn slightly more than $ 12,000 a year in revenue.

What immediately jumps through the photo 's on Dollar Street is how remarkably the same daily life is around the world, with the exception of the very rich and poor. The vast majority of households have electricity, water in the house, children who go to school and some sort of transport.

"The most striking thing is that so many people we've visited so far actually have a plastic toothbrush," said Rönnlund, who started Dollar Street in 2015. "It's the same with soap, almost everyone in the world has access to some kind of toothbrush, the poorest buy a small part of a soap bar or make it yourself." When you come to the center, you see people locally-produced, large pieces of soap The higher your income scale, the better the soap becomes – or even multiple cleaning products. "

That ties in with Kharas's research. "These people in the global middle class have many things in common," he said. "They like air conditioning, a refrigerator, a car or a motorcycle to move around, and they enjoy going on holiday and do not have to work every day."

5. Does more money and more things make us happier?

There are endless discussions about how much money and which lifestyle would maximize happiness. The consensus among researchers who have studied this extensively is that the daily mood does not improve much after about $ 75,000 per year in the United States. There is not much noticeable improvement in mood afterwards, even when houses and bank accounts grow. That said, people also feel better when they go up the income ladder, do not go down or get stuck, which helps explain why the middle class in the United States and a large part of Europe is upset after years of stagnating income.

Ronnlund and her team have witnessed some of these trends with the Dollar Street project. They do not specifically ask for happiness, but they have asked every family they photographed about their favorite things they own and what they would like to buy if they had a little more money.

A poor family picked up a plastic bucket as their favorite possession because it was the difference between life and death for them. They dreamed of getting a phone or a better bike. Families from the middle class valued things that made their lives better, such as air conditioning or a fridge, and they wanted to own cars or houses. Richer families appreciated items such as special alcohol, exotic plants or beautiful stuffed unicorns.

"I thought it would be easiest to photograph rich people, but it was the opposite," Rönnlund said. "Richer people find it harder to make people come home as they are, they want to present it in the right way so that they look good and present the social media version of themselves."