[dingfeng_quek]

According to the paper, there's a decrease in demand by the primary home device for activities trackable by comscore. This is the data used (not technically an assmption). I do not see the paper claiming more than this.

The conclusions do not apply to aggregate demand from all device types. Only certain types of activities are tracked.

My personal opinion is that the inferiority of online time is due to the increase in use of and substitution to additional devices and apps that were not tracked in the dataset - and a higher income better affords such alternative devices, apps, and their data plans.

[dahart]

Yes, exactly - I agree with your opinion and was suspecting the same, that substituting additional devices may explain the results.

But if untracked devices are responsible, or simultaneous online usage by multiple household members is responsible, then doesn't that mean it's possible that online time is not an inferior good? Couldn't it even be opposite of that, that higher income households are actually online more than lower income, because they have more devices, and don't use the primary home device? It seems likely to me that the idea of a primary home device applies more to, and affects more people in lower income households.