## Info Mapping : the "7 +/- 2" rule

Subject: Info Mapping : the "7 +/- 2" rule
From: Frederic Wronecki <frederic -dot- wronecki -at- WANADOO -dot- FR>
Date: Thu, 5 Sep 1996 09:12:42 -0700

The "Seven plus or minus two" rule is a statistical result (Gauss
"bell-shaped" curve) which can be expressed this way, supposing a nice
theoretical curve :
- 18 % of readers can handle 4 mental units or less ;
- 12 % can handle 5 units ;
- 13 % can handle 6 units ;
- 14 % can handle 7 units ;
- 13 % can handle 8 units ;
- 12 % can handle 9 units ;
- 18 % can handle 10 units or more.

Then if a 9-step procedure must be remembered and performed, the chances
are that about 18 + 12 + 13 + 14 + 13 = 70 % (yes : 70 % !) of the
operators will fail or ask for assistance from time to time. With a
7-step procedure, the risk would be 43 %, and with a 5-step procedure, it
would fall under the acceptable value of 18 %.

Besides, remember that it has been observed that if a long list of items
is presented to people who have to remember it, they will tend to better
memorize the beginning- and the end- items. In other words, the items in
the middle of the list are much more likely to be forgotten.

So the question shifts from "what is the maximum number of items" to
"which level of risk can you afford ?".
--
Frederic Wronecki
France Telecom, Paris, France
mailto:frederic -dot- wronecki -at- wanadoo -dot- fr

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