Magical Numbers: The Seven-Plus-or-Minus-Two Myth
http://www.ieeexplore.ieee.org/iel5/47/21669/01003695.pdf
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  peer-reviewed

Doumont, Jean-luc
IEEE Transactions on Professional Communication
2002

Abstract:

George Miller’s “magical number seven, plus or minus two” is poorly understood and, consequently, blindly applied to professional communication. As an example, I have heard speakers explicitly allow themselves up to seven items of up to seven words on each visual aid, in addition to the title. Any such slide would fail any real-life test of effectiveness, such as briefly showing the slide while going on talking, then asking the audience what was on it. Such misconceptions endure.