Minimizing the Effects of Uninteresting Factors

• Show some pictures with a subliminal cue, and some without, and count how many are correctly recognized.

  Which pictures are shown in which condition?

We are presumably not interested in discovering that:

• some people have better memories than others
• some stimuli are more memorable than others

Even with a balanced design, though, you may find that you need quite a few trials and quite a few subjects to get good data.

Be prepared for the potential scope of your experiment!