Gapminder's Dollar Street and the role of self-supply
On Gapminder's website they write


  If you have a question, maybe it's already answered in our Q&amp;A.
   Q&amp;A


The underlined text links to a Google document, which answers several questions. Under one of these answers


  The households’ door numbers represent the consumption values (US dollars) that each adult in the household has per month. This figure comes from a combination of the household’s self-reported consumption and income levels. We then checked official cost of living data in each country to adjust the values for purchasing power parity (PPP) and converted the value into US dollars.


there is a link to a further Google document titled Detailed income calculations for Dollar Street. This second one seems to answer your question, but it is several pages long, so I will not copy paste its full body of text here.