Bill Gates may be on a mission to eradicate extreme poverty, but he's not going to do it by focusing on the "developing" world anymore.

"I talk about the developed and developing world all the time, but I shouldn’t," Gates wrote in a new blog post this week.

His new resolution to eradicate "developing" and "developed" from his vocabulary was spurred by the release of the book "Factfulness," written by his good friend and Swedish statistician Hans Rosling. Rosling died of pancreatic cancer last year, bit his book is out post-mortem, after his son and daughter-in-law finished the final pages for him.

Gates called it "one of the most educational books I've ever read." and said the world would be better if millions of others read it, too.

Factfulness is Rosling's final attempt to change the fatalistic ways that he says most people view the world. He wants us to know that statistically speaking, things aren't as bad as we might think. He believes we rely too much on a set of emotion-fueled "instincts" to frame the state of the world, painting a much gloomier-than-reality picture of everything from global education to healthcare and natural disasters.

One of the biggest ways he hopes to do this is by replacing the binary framework of one "developing" world pitted against another "developed" world.

Instead, he says it's more useful (and accurate) to think of world income levels in four distinct brackets. While someone living in Level 1 might use their fingers to rinse and brush their teeth each night, a person living in the Level 4 income bracket would more likely plug their electric toothbrush in for a charge when they're done sudsing up their pearly whites.

But it's not just Rosling who's changing his global income vocabulary. The World Bank now uses a similar four-tiered system to talk about income levels, too. And Gates wants to be next.

"I’m going to try to use this model moving forward," the billionaire philanthropist wrote on his blog Tuesday.

Here's how the four global income levels break down:

Level 1: People live on less than $2 a day. Rosling estimates that one billion people are living at or below this threshold. They get around on their own two barefoot feet, cook over an open flame like a cookfire, fetch water in a bucket, and sleep on the ground.

Some people living in countries like Nepal, Madagascar and Lesotho all fall into this income category.

Lesotho, Rosling says, has the lowest life expectancy of any country in the world.

Level 2: This is the income group where the majority of the world's people live. They get by on between $2 and $8 a day and might have some possessions like a bicycle, a mattress, or a gas canister for cooking at home.

Countries like Bangladesh, China, Zambia and Nigeria all have people living in this income level, but of course many Chinese and Nigerian people have much higher incomes, especially if they live in big cities.

That's one of the reasons that Rosling argues it's silly to lump entire countries and sections of the world into broad categories like "developing" versus "developed." It's meaningless.

Level 3: This is the second most populous category on Rosling's list, after level 2. People in level 3 live on anywhere from $8 a day to $32. They have running water, might own a motorbike or car, and their meals are a rich and colorful mix of foods from day to day. They also probably have electricity and a fridge, which makes things like studying and eating enough varied nutrients easier.

Egypt, Palestine, the Philippines and Rwanda all have citizens living on this level.

They might have enough money to take small vacations, and their children are generally free to finish high school, because they don't have to drop out early to make money for their family.

Level 4: Like level 1, roughly one billion of the world's people live on this level. They make $32 a day or more and have things like running water (both hot and cold) at home, a vehicle in the driveway, and plenty of nutrients on their plate. They've also likely had the chance to finish twelve years of school, or more.

Just about anyone living in the US, Mexico, South Africa, Sweden or South Korea is going to fall into this income category.

It includes essentially all of what people think of as the "developed" world, but accounts for roughly one-seventh of the global population.

Be cautious about assuming that your level is the best, or most "normal'" level, Rosling says.

"Be cautious about generalizing from Level 4 experiences to the rest of the world," Rosling writes. "Especially if it leads you to the conclusion that other people are idiots."

People around the world are coming up with ingenious ways to solve their problems on every level, every day. Rosling cites the example of visiting one family in Tunisia whose house is in a continuous state of construction.

"In Sweden, if someone build their house like that, we would think they had a severe planning problem, or maybe the builders had run away," he writes.

Rosling says the reason their house is always being constructed is because without easy access to a bank, it's the best way for the Tunisian family to safeguard their wealth. Unlike a pile of money, a pile of bricks being slowly cemented into a home can't be easily stolen.

"When something looks strange, be curious and humble," Rosling adds. "Think, in what way is this a smart solution?"

And remember, "leveling up'" isn't always a good thing.

Just because someone's not living on the tippy-top Level 4 doesn't mean they're living an unfulfilling, deprived life.

Rosling says that a full 80% of the world's people have some access to electricity. That means people on levels 2, 3 and 4 are all taking advantage of some current every day. Of course, that doesn't mean they're flipping off a switch every night when they go to bed, but at some point in their daily life, they're plugging in and getting what they need, whether it's at home, work, school or elsewhere in town.

Meanwhile, people living in Level 4 aren't doing everything right. They have by far the highest CO2 emissions levels of anyone on the planet. As Rosling notes, Canada's per capita CO2 emissions are today "twice as high as China's and eight times as high as India's." Together, people living on income Level 4 burn more than 50% of the fossil fuels consumed on Earth each year.