"The monotonic negative relationship between income and total time suggests online attention is an inferior good."
To my eyes, this seems to be drawing a causal conclusion, and implying a negative judgement. I might be mis-interpreting use of the word 'inferior' here, but later in the paper, references to inferior seem less sensational to me.
"we also observe “attention inferiority,” decline in the amount of online attention with higher income."
"We find further evidence for persistent attention inferiority, namely, that higher income households spend less total time online per week."
Those seem to say inferior == less, whereas the first one seems to suggest that the Internet is less valuable to higher income people. Am I off base?
"We are limited in our ability to draw conclusions about the total time spent online by a household across all devices, and we possess no information about which household member spent time on the PC in multi-dweller households."
So, they make a lot of noise about higher incomes spending less time online, and yet one possible explanation is that higher income families have more devices and spend time online simultaneously, whereas lower income families have to serialize their use.