That's not how double blind studies work.

You misunderstood my point.

I didn't claim the participants wouldn't know whether they own a phone - obviously they would. I said they wouldn’t know they’re in a study whose purpose is to correlate smartphone use with academic performance.

That's perfectly compatible with a double-blind setup:

* the *students* just think they’re taking standardized tests, not that the effects of their smartphone habits are being monitored;

* the *graders* don’t know whose tests belong to whom.

That’s about as "double blind" as social-science research gets. The commenter I replied to latched onto the literal impossibility of hiding the phone itself, not the intentional design of the experiment.

Ok. My understanding of double blind studies is that they involve a placebo. I don't really want to argue about social science experiments.