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Insights from Human Factors International
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In This Issue Bob Bailey reviews:
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Reducing reliance on superstition
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How to improve design decisions by reducing reliance on superstition.
Let’s start with Miller’s "Magic 7"
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Probably the most well-known article in the fields of usability, user
interface design and user experience is Miller’s 1956 paper entitled
"The magical number seven, plus or minus two." It is incredible
how this article has lasted for over 40 years, and still seems to influence
many design decisions. More recent, better research is available, but
not being used.
I recently re-read the 16-page article, and have concluded that there
is absolutely nothing in his paper that can still help us develop better
systems. I am not attacking George Miller. Miller was an excellent researcher
and added much to our knowledge in the field. I am addressing the unfortunate,
continued success of this one paper.
At least partially because of the success of Miller’s paper, the
number "seven" is now almost universally and erroneously accepted
as the human capacity limit for a wide range of issues. I have had people
tell that the "Magic 7" paper is the reason why the local telephone
number has seven numbers. This is not true. I have had others tell me
that the "Magic 7" paper is the reason they:
- place only seven items on the menu bar,
- place only seven items in a pull-down menu,
- have only seven bulleted items in a list,
- never have more than seven radio buttons or check boxes together,
and
- place only seven tabs at the top of a website page.
These are all silly decisions, and I suspect that Miller’s "Magic
7" paper continues to cause many other poor design decisions to be
made. For example, a designer thinking that it is okay for people to remember
a few items shown on one Web page while waiting for another page to load;
after all (the designer reasons), "the research shows that people
easily can remember seven items for a little while." More recent
research indicates that people can remember closer to 3 or 4 items for
a short period of time.
When Miller published his paper in 1956, most scientists believed that
there was only one human memory system. The idea of a separate "short-term
memory" system was not generally known or accepted, and there was
no understanding of short-term memory’s characteristics, uses or
limitations. This gradually changed in the next couple of years with the
work of Brown (1958) in England and Peterson and Peterson (1959) in the
United States.
In the early 1970s, investigators began broadening their view of short-term
memory to a more useful one that became known as "working memory."
The current concept of working memory describes a memory system that does
more than just temporarily store small amounts of information. For example,
having a greater working memory capacity is positively related to increased
reading comprehension, drawing inferences from text, learning technical
information and reasoning skill (Baddeley, 1992).
Even though the field has systematically moved from Miller’s "immediate
memory," to "short-term memory," and currently to "working
memory," many practitioners are still back in the 1950s. Even Miller’s
original "seven" has been shown to be untrue. For example, Broadbent
(1975) suggested that the working memory capacity was actually 4-6 items,
MacGregor (1987) reported that it was only four items, and LeCompte (1999)
argued that it was actually about three items.
The next time you read or hear someone refer to Miller’s "Magic
7" paper as the justification for their argument, quietly say to
yourself, "Oh-oh, the amateurs are at it again."
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References
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Baddeley, A. (1992), Working memory, Science,
255, 556-559.
Broadbent, D.E. (1975), The magic number seven
after fifteen years. In A. Kennedy and A. Wilkes (eds.), Studies
in Long-Term Memory, New York: Wiley, 3-18.
Brown, J. (1958), Some tests of the decay theory
of immediate memory, Quarterly Journal of Experimental Psychology,
10, 12-21.
LeCompte, D. (1999), Seven, plus or minus two,
is too much to bear: Three (or fewer) is the real magic number,
Proceedings of the Human Factors and Ergonomics Society, 289-292.
MacGregor, J.N. (1987), Short-term memory capacity:
Limitation or optimization? Psychological Review, 94(1), 107-108.
Miller, G.A. (1956), The magical number seven,
plus or minus two: Some limits on our capacity for processing information,
The Psychological Review, 81-97.
Peterson, L.R. and Peterson, M.J. (1959), Short-term
retention of individual items, Journal of Experimental Psychology,
58, 193-198.
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Past Issues
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