7 + - 2???
3 or 4???
Those of you who have been in the field of usability or user experience for a few years have probably heard the phrase “The Magic Number 7 Plus Or Minus 2″. This refers, actually, to what I would call an urban legend. Here’s the legend part:
Legend: “A guy named Miller did research and wrote a research paper showing that people can remember from 5 to 9 (7 plus or minus 2) things, and that people can process 7 plus or minus 2 pieces of information at a time. So you should only put 5 to 9 items on a menu, or have 5 to 9 tabs on a screen”.
Have you heard this? If you’ve been reading about usability for a while I’m sure you have. Well, it’s not quite accurate. Another guy named Baddeley questioned all this urban legend. Baddeley dug up Miller’s paper and discovered that it wasn’t a research paper, it was a talk that Miller gave at a professional meeting. And it was basically Miller thinking out loud about whether there is some kind of inherent limit to the amount of information that people can process at a time.
Baddeley conducted a long series of studies on human memory and information processing. And what he concluded is that the number is 3 to 4, not 5 to 9.
You can remember about 3-4 things (for about 20 seconds) and then they will disappear from memory unless you repeat them over and over. For example, let’s say you are driving in your car and talking on your cell phone (ok, you shouldn’t be doing that) and someone gives you a number to call. But you don’t have a pen handy, and anyway you are driving. So you try to memorize the number long enough to hang up from one call and dial the new number. What do you do? You repeat the number over and over (putting it back into short term memory each time, which buys you another 20 seconds). The interesting thing about phone numbers is that they are more than 3 or 4 numbers long. So they are hard to remember for more than 20 seconds.
712-569-4532
We also tend to chunk information into groups that have 3-4 items in them. So a phone number in the US is: 712-569-4532. Three chunks, with 3-4 items in each chunk. If you know the area code “by heart” (i.e., it’s stored in long term memory), then you don’t have to remember that, so one whole chunk went away. Phone numbers used to be easier to remember because you mainly called people in your area code, so you had the area code memorized (plus you didn’t even have to “dial” the area code at all). And then if you were calling people in your town each town had the same “exchange” — that is the 569 part of the phone number above. So all you had to remember was the last four numbers. No problem! I know I’m “dating” myself here by telling you how it used to be back in the old days. (I live in a small town in Wisconsin, and people here still give their number out as the last four digits only).
But that’s not all! Researchers working in the field of decision-making tell us that people can’t effectively choose between more than 3 to 4 items at a time.
So, what does all this mean? Can you really only have 4 items on a navigation bar? or 4 tabs on a screen, or 4 items on a product detail page at an e-commerce web site? No, not really. You can have more, as long as you group and chunk.
Here’s an example: At the Upton Tea site they have lots of tabs, but the tabs are not chunked into groups of 3 or 4.
So people will tend to do a partial scan and not even look at or read all the tabs. (I love their teas, by the way.. just wish they would do some work on the layout and emotional aspects of their site, but that’s probably another blog!).
I’ve covered more than 4 items in this blog post, so I’ll stop now! For those of you who like to read research here are some references:
- Baddeley, A. D. (1986). Working memory. New York: Oxford University Press.
- Baddeley, A. D. (1994). The magical number seven: Still magic after all these years? Psychological Review, 101, 353-356.
- Miller, G. A. (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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Susan, this is an excellent series with really interesting and useful information. Thank you and please keep it up!
Thanks for writing this, I keep reading about the Magic 7 far too often!
One thing I’d like to add is, that the amount of time, that one is able to keep chunks within the working memory depends on the amount of chunks and the size of the chunks themselves. Both of these dimensions influence the time of rehearsal and thereby limit the time it can be kept from forgetting (Card, Moran, Newwell (1986)).
Cheers.
Great point Frederik and thanks for the Card reference.
There is no need for people to remember the items they *see* on the screen, so whatever is the correct number, I find using it in this context questionable. I would rather apply those limits to mouse/touchscreen gestures, complicated keyboard shortcuts etc.
Mekk,
Thanks for commenting.
People do sometimes have to remember something from one screen to the next, so I think it’s still relevant to talk about remembering things on a screen. Besides remembering there is also the idea of just having to process more than 3-4 things or deciding amongst more than 3-4 things. The larger point I was trying to make is that 3-4 things is the magic number rather than 5-9 things.
But yes, I do agree that there are many other places that the 3-4 consideration should be applied.
[...] Which Table Resulted in More Tasting? You would think that people would taste more jam when the table had twenty-four different varieties. But they didn’t. People tasted only a few varieties whether there were six or twenty-four choices available. People can only deal with 3 to 4 things at one time (see the post on 100 Things You Should Know about People: #3 — You Can Only Remember 3 to 4 Things At A Time (The M…). [...]
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In your book you say that more options means more attention but less convertions. I think category pages should list a last 6 options, extra work of pagination is not good for user. Large navigation schemas vs long category pages.
[...] for a fraction of a second before you start reading the stuff that you really came for. And because your short-term memory is only able to hold onto stuff for about 20 seconds, the bearded fella will quite literally be out of your mind before you’ve read halfway down the [...]
Just because people tend to only remember 3-4 items at a time in their short term memory should not be reason to group menu items in groups of 3-4. Because the menu items are always on the screen, there is not need to remember them, rendering the theory mostly useless. There may be other reasons that groupings of 3-4 could provide better usability, but it’s not because of memory, because we don’t need to remember it if it’s always in front of us to reference when needed.
I remember only having to dial 4 digits to call our neighbors. Grew up in Dewey, AZ. This also reminds me of going to the little general store. Picking out a candy bar was simple and quick since you only had one small isle of candy to choose from. Same with buying a soda, root beer, orange or pepsi.
Now I go into the candy isle(s) and it takes forever to decide, even for a creature of habit. The pre-frontal cortex is on overload at the local 7-11.
Interesting ….
[...] People remember only four items at once #28/#60 Some types of mental processing are more challenging than others #53/#08 Unpredictability [...]
Remembering 3-4 things and Selecting 3-4 things.
My friend’s father had a chain of hardware stores. He only had 3 variants of each item in his store. 3 types of TV’s, 3 radio’s, 3 stereo sets, 3 washing machines.
That made life easy for both his sales rep’s and for his customers.
The psychological tendancy is to choose the middle option of 3. So make the middle option slightly less expensive as the most expensive one. E.g. 1,25 euro; 2,25 euro and 2,50 euro. Thus you maximize your business.
This is complete nonsense. It’s one thing to remember things, it’s a completely other to view and choose between things that you don’t need to remember. If you let UI design be controlled by the 3-to-4 rule you’ve obviously completely missed the point of how humans perceive things (perception is something else completely).
Teardigrade — Perception is different, but when people are perceiving things in a UI design they aren’t just visually perceiving them. They have to decide about them, think about them, compare them…
I’m not saying you can only have 3-4 things in any part of your UI, but you need to realize that people will only be dealing with 3-4 at any one time.