Experiments in human psychology are often conducted with en elaborate ruse to hide the real purpose from the subjects. The infamous Milgram Experiment, for example, was disguised as a test of the effectiveness of corporal punishment on students or something like that. The real purpose was only revealed after the experiment.

I don't know what kind of disguise they used with the dice experiment, but the earlier version using matrix quizzes could be easily disguised as a test of math skill relative to the time of day. (Subjects who are prone to cheat might try to look smarter than they actually are, but this actually plays perfectly into the researchers' goal!)

Fun project: Go to a large research university and look for flyers asking for people to participate in psychology experiments. Read the description and try to guess what those experiments are really about.