The Magical Number Seven, Plus or Minus Two
The number indicates the Miller A. Miller determined by George fact that a man is only 7 ± 2 units of information ( chunks ) can hold in short-term memory present. The size of the short-term memory is genetically determined, and may also be "Training " can not be increased. The written this regard by Miller article The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information is one of the most cited articles in the field of psychology.
The seven- phenomenon
John Locke already discovered over 300 years ago the so-called seven phenomenon, as he examined the uptake of an adult. He found that subjects who see a greater number of objects for a brief moment and then remember these must, at up to 7 objects have a hit rate of almost 100 percent. More than 7 objects there is a sudden drop in the rate. We are thus able to repeat later after only one short Watch up to seven chunks short time, but rarely more.
The average capacity is 6 to 7 chunks. A short-term memory of 8 chunks were already above average.
Impact in practice
Methods for dealing with complex systems (see Fredmund Malik, requirements management, software engineering ) always aim from the disassembled into manageable chunks. The limit of the manageable size is often achieved upon reaching a number of system elements 7.
This results in different effects and recommendations can be explained:
- Hierarchies are ineffective if more than 7 people in a plane have a direct supervisor.
- If more than 7 goals are pursued simultaneously, the overview is lost.
- Meetings with more than 7 participants lose efficiency.
- Project groups without losing hierarchical structuring of 7 or more strongly to efficiency.
- An outline level in documents should not have more than 7 sub-headings.
- A website should have a maximum of 7 navigation points.
- In programming, a method should not have more than 7 parameters.
- In object-oriented development of a class should not have more attributes than will fit in the short-term memory of the developer. Likewise, class hierarchy levels should be restricted.
- In Scrum, a process model of agile software development 7 ± 2 is specified as the ideal size for a team.
- A group is for the individual member only manageable if it consists of a maximum of 7 other people besides him: A squad is the smallest military outline form and consists of a maximum of 8 men.
- A contubernium, the smallest organizational unit in the ancient Roman army consisted of 8 men.
Criticism
The focus on the number seven as a phenomenon is dubious even by the original experiments of Miller, ibid since the full restoration identification numbers at 7, 6 and 5 letter words were, so depending on the type and is especially length of the chunks. Baddeley suggested later that the working memory is not limited by the number, but after a time, so that all chunks that are sprechbar in two seconds, can be fully processed. In the further research of Baddeley could be shown that related chunks can be easily noticed, so the experiment also sets of 15 words and can be accurately reproduced more each. On the other hand, shows that a lower limit is already occupied by simultaneous detection of 4-5 chunks.
Research of the University of Missouri, where the experiment was repeated with symbols, revealed that the man can keep an average of only 3 to 4 chunks of information in working memory.