17 January 2012

How many items should go in a menu?

This article was first published on 29 January 2005.

How many items should go in a menu?


A lot of people think 7 ± 2 (i.e., between 5 and 9, with a preference for 7).

NO! It isn’t! And here I will explain why. But first I have to give a very short history lesson…

Miller (1956)

In 1956, Miller performed what has become a seminal experiment: he gauged the capacity of short term memory. What he found was that people could hold 7 ± 2 items in their memory (i.e., 5 to 9, tendency towards 7). This was astounding because nobody had before managed to define the limits of memory like this before.

Research expanded upon this somewhat (which is an understatement). For example, later research found evidence of “chunking” - people could remember more than 9 items if they managed to gather some items together into “chunks". Since then, an awful lot of work has been performed on it, and short term memory is still very much a hot topic in psychology.

But what has this to do with the number of items on a menu? Well, the thinking is that if a person can memorise 7 ± 2 items, then that is what should be in a menu. That’s the maximum amount that can be retained in short term memory without it being “processed” into long term memory.

Passing information into long term memory is a different process: consider short term memory as something like a cache: easily accessed, very fast, but just not there for long because there isn’t enough to go around. Long term memory by contrast is like saving something on a slow medium (like floppy disk, but many times larger). It’s slow, will probably take several tries, and it can be hard to get it back.

My brain hurts…

This sounds all well and good, but there are major problems. This is why:

If I perform a task using a computer, I have things in my short term memory. Maybe I want to copy a few words in a text editor and paste them somewhere else. I don’t want to commit this to long term memory: firstly it’s a waste (why would I want to remember this in several years time?), and secondly it’s slow. So I use my short term memory.

However, this is occupied with a few things already. Firstly what I am trying to do: what kind of document am I trying to create? Secondly, I want to remember what I want to move (and maybe I want to remember why as well). Thirdly, I want to remember where it is to be moved to (and maybe why as well). This list goes on.

You may have noticed that I need to keep these things in my memory. As I am sure you have experienced, you may forget why you are doing something in the middle of doing it. It’s awkward and slows you down, so it’s best to keep it “live” in the mind.

But with all these things floating around, surely my memory capacity is reduced? Well, put simply, yes it is. But if the theory behind 7 ± 2 items is correct, showing someone a menu with 9 items will cause them to entirely forget what they were doing, why they were doing it, and how. Is that really the case? It isn’t - I can look at a long menu and still remember exactly what it is that I was doing (in most cases!).

Recall versus recognition

Recall is when someone remembers something without any sensory prompt: recognition is when there is some prompt available.

For example, if I asked you in what year were you born, the chances are that you could recall it. However, if I asked you some obscure question about an API, you might not be able to tell me the answer ("it’s on the tip of my tongue!"), but if I gave you a hint (such as the name of a function) it would all come flooding back. That is recognition.

The 7 ± 2 items assumes that no long term memory is used when using a menu. However, menus rely on two different modes of cognition: recognition, and exploration.

As I explained, recognition relies on having a sensory prompt: the list of possible commands provides hints as to what can be done without needing to recall the exact command (which is why clearly defined menu actions are so important). With exploration, users can just guess at the best option and try it out, but that isn’t the issue here.

When people use menus, they rely on recognising the command: users who know the command but don’t know where it is can be seen searching for it, or examining the top level menu items for a hint. However, it is false to say that one “chunk” of memory is used for each menu item. I can look at a menu of 12 items and remember my original task.

I’ll look into the number of items in a future article.

References

Howes, A. (1994). A model of the acquisition of menu knowledge by exploration. In W. Kellog & T. Hewett (Eds.) Proceedings of the ACM Conference on Human Factors in Computing Systems CHI’94. Boston, MA. New York: ACM.

Miller, G. (1956). The magical number seven plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63, 81-97.
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