https://www.brookings.edu/blog/future-development/2018/09/27/a-global-tipping-point-half-the-world-is-now-middle-class-or-wealthier/?utm_source=newsletter&utm_medium=email&utm_campaign=sendto_newslettertest&stream=top

We make these claims based on a classification of households into those in extreme poverty (households spending below $1.90 per person per day) and those in the middle class (households spending $11-110 per day per person in 2011 purchasing power parity, or PPP). Two other groups round out our classification: vulnerable households fall between those in poverty and the middle class; and those who are at the top of the distribution who are classified as “rich.”

Our “middle class” classification was first developed in 2010 and has been used by many researchers. While acknowledging that the middle class does not have a precise definition that can be globally applied, the threshold we use in this work has the following characteristics: those in the middle class have some discretionary income that can be used to buy consumer durables like motorcycles, refrigerators, or washing machines. They can afford to go to movies or indulge in other forms of entertainment. They may take vacations. And they are reasonably confident that they and their family can weather an economic shock—like illness or a spell of unemployment—without falling back into extreme poverty.

Gotta love capitalism, giving people with awesome ideas a way of fulfilling them then create jobs for other is why it's awesome. Most people work towards being rewarded for their work, no one is going to work towards having their rewards forcefully taken from them

so anyone earning more than $110 a day is not middle class but rich, Wow Everyone I know is a member of the rich class

What a complete bullshit graph. I can assure you that at least half of Bangla Desh and India falls into the "poor group", whatever way you want to define "niddle class".
Bad Science operating at its worst.

i get/spend 3300 a month, in my country, if you not have over 5500 you not middle class, the minimum vital for live in my country for politic is like 4000, so this study not worked on all country for sure.

$110 a day is rich? Shouldn't that go into yhe vulnerable section?

$11/day is about $330/month, which is well below the poverty line in Australia, which is roughly $1876/month.

Even the homeless in Australia would spend more than $11/day. These numbers are complete garbage.

That's not rich, that's middle class. 12k isnt going to get you much. You're not going to be able to afford vacations throughout the year (maybe you'll be able to squeeze out a few weeks a year) You can't afford a second vacation house or even a first house or condo in a nice urban area like Manhattan, Toronto etc. You cant afford a decent boat, luxury hotels (except for a few days) etc. 12k gets you nothing except a roof, food and some local entertainment.