Miller’s Magic Number and It’s (Non-) Relevance to Web Navigation
At some point, anyone working on the web has heard the exhortation that ideal web navigation should be “seven items, plus or minus two” with some vague reference to science which “proves” this is true.
Some years ago, I finally decided to look up the “science” and found that this is a reference to what’s been called “Miller’s Magic Number,” which come from an article by George Miller published in the Psychological Review in 1956. The article was entitled “The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information” (link to original text).
This weekend, I finally took the time to read the article. It’s dense, but in it, Miller summarizes dozens of studies that examine (1) the ability of humans to remember information, and (2) the ability of humans to distinguish between gradients of information (so, to evaluate something – an audio tone, in one example – and correctly categorize it). He summarizes the research to mean that our ability to do these things across all these different studies fell to somewhere around seven items.
I was bothered by what I found. The more I read both the article and multiple summaries of it, the more I became convinced that this has nothing to do with web navigation. It just didn’t seem to follow – I don’t memorize web navigation, nor do I compare it to a gradient scale. All the studies Miller discussed seem to do with recall and categorization. I couldn’t figure out what this had to do with anything.
I was all set to write a passionate post to his effect…and then I found that someone had beat me to it:
UX Myth #23: Choices should always be limited to 7+/-2
Limiting the number of menu tabs or the number of items in a dropdown list to the George Miller’s magic number 7 is a false constraint. Miller’s original theory argues that people can keep no more than 7 (plus or minus 2) items in their short-term memory. On a webpage, however, the information is visually present, people don’t have to memorize anything and therefore can easily manage broader choices.
That’s a well-written post that summarizes about a dozen references which refute the link between anything Miller ever did and the design of web UI and navigation.
Bottom line: the “magic number 7” has nothing to do with web navigation, and only may have some application to larger concepts of IA. If someone quotes it, they’re just likely just repeating something they’ve heard and have never actually read the primary research on it.
This is sadly common – things that make a good sound bite tend to take on a life of their own. We repeat these things because they sound smart and reinforce some narrative which makes sense in our heads. They provide form to an amorphous concept which we hope has discoverable boundaries, so when we find something that claims to define one such boundary, we pin our hopes on it and are loathe to let it go or even examine it too hard lest we threaten it. From there, these things propagate like a virus.
Larger lesson learned: make an effort to read and evaluate original sources, which I’ve argued in favor of before. If you hear something like this, trace it back to see whether the original research actually exists and whether or not it supports the conclusion.