Miller’s number 7 ± 2: Psychology Myth Busting #2

Second in a series of Psychology Myth Busting.

A common myth within psychology and design based on a misinterpretation of work by Dr George Miller. It’s often used to say how many items should be in a navigation menu.

Miller looked at the capacity of a part of human memory called working memory; that is, the memory we use to hold multiple pieces of information temporarily while we process them.

This research is often referenced incorrectly. It has been widely and inaccurately reported that Miller stated that human working memory can hold seven plus or minus two items. Miller himself wrote way back in 1956 that he had been “persecuted by a integer”, yet I still hear the 7±2 myth being cited today.

Even George Miller was shocked to see how badly his original concept was misinterpreted, saying that:

The point was that 7 was a limit for the discrimination of unidimensional stimuli (pitches, loudness, brightness, etc.) and also a limit for immediate recall, neither of which has anything to do with a person’s capacity to comprehend printed text.

Interestingly as of November 20, 2014 Wikipedia also gets it wrong or I should say doesn’t highlight the criticism of the theory.

Short Term Memory vs Working Memory

There’s even dispute as to the basis of short term memory. I prefer the concepts associated with Working Memory, that is memory that’s used to process ideas, concepts and well, things. Typically working memory is goal focused whereas short term memory is about recent sensory inputs. Here’s a great overview of Working Memory.

Hick’s to the rescue

If we want to quote an ‘ideal’ number of items to display in a group we can use Hick’s Law to work out what we should do.

Hick’s Law is a measure of number of choices offered and time. Time being a substitute for thinking. Less stuff, less thinking, quicker choice. Use it to work out how many items to display that you want someone to make a considered choice between. Here’s an article on applying Hick’s Law

Death to bullshit science

The conclusion, always question psychology theory when it’s applied to design or design people.

1. Maslow’s Hierarchy of Needs – Favourite of the ad agency
2. Miller’s number, 7 ± 2 – Haunted by a number
3. Left Brain / Right Brain – What? You can’t be creative and code?
4. Myers Briggs – No better than a Buzzfeed quiz

If you want to learn how to evaluate psychology theory and apply it to design and user experience, you should come to one of my workshops. Learn more and sign up to the email list.