[christinecha]

I really want to know how the conversation went with the folks in the control group.

"Hey, we're doing a study where we give money to a bunch of people... Not you, though."

Ha!

[Rinum]

The control group could be blinded (they're unaware what is being studied).

[jamesjyu]

They just get Monopoly money ;)

[Fomite]

There are a number of study designs that don't require a null-intervention control group. Some of those would have been interesting, and might actually have yielded something closer to the true effect.