This does not mean that changing from tabs to spaces will increase ones income.
I would expect there simply is a confounding factor that the author did not look at. Maybe the info is not in the data.
I can imagine that the space/tab choice is related to the "upbringing" of the developer. Maybe which language or editor they used first in their life.
Or maybe it's related to culture. For example when using IRC, tabs are usually not used to communicate. Maybe that impacts the general choice of tabs/spaces.
Or maybe more sophisticated users tend to exchange the tab key for something else:
I would expect there simply is a confounding factor that the author did not look at. Maybe the info is not in the data.
I can imagine that the space/tab choice is related to the "upbringing" of the developer. Maybe which language or editor they used first in their life.
Or maybe it's related to culture. For example when using IRC, tabs are usually not used to communicate. Maybe that impacts the general choice of tabs/spaces.
Or maybe more sophisticated users tend to exchange the tab key for something else:
https://xkcd.com/1806