You can find their methodology
here. That page states:
Quote:
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The Global Rich List calculations are based on figures from the World Bank Development Research Group. To calculate the most accurate position for each individual we assume that the world's total population is 6 billion¹ and the average worldwide annual income is $5,000².
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So yes, they're using quick and dirty calculations, but I suspect it's about as reasonably accurate as you could hope for.
Based on the table on that page anyone making over $47,500 is in the top 1%. Even if that's way off and such a person is only in the top 10%, it still conveys the message that most of us are a lot better off than we realize.
