Overview

Many designers have most likely heard of Miller’s Law, and there is also a high probability that what they understand about it is inaccurate. This commonly misunderstood heuristic has frequently been cited as justification for design decisions such as “the number of navigation items must be limited to no more than 7” and so forth. While there is value in limiting the amount of options available to users (see Hick’s Law in chapter 3), it is misleading and inaccurate to attribute such dogma to Miller’s Law. In this chapter we’ll explore the origins of Miller’s ‘magical number 7’ and the real value Miller’s Law has to provide UX designers.

Origins

Miller’s Law originates from a paper published in 1956 by cognitive psychologist George Miller title “The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information"1. Miller, a professor of Harvard University’s Department of Psychology, discussed in his paper for Princeton’s Psychological Review the coincidence between the limits of one-dimensional absolute judgment and the limits of short-term memory. Miller observed that memory span in young adults was limited to approximately 7, regardless of the stimuli consisting of vastly different amounts of information. This led him to the conclusion that bits, or the basic unit of information, doesn’t affect memory span as much as the number of information ‘chunks’ being memorized. ‘Chunks’ in cognitive psychology refers to collections of basic familiar units that have been grouped together and stored in a person’s memory.

Miller’s paper is often interpreted to argue that the number of objects an average human can hold in short-term memory is 7 ± 2. Later research on short-term memory and working memory revealed that memory span is not a constant even when measured in ‘chunks’. Miller himself only used the expression “the magical number 7” rhetorically and acknowledged the correspondence between the limits of one-dimensional absolute judgment and of short-term memory span was only a coincidence.

Key Concept: Chunking

Miller’s fascination with short-term memory and memory span centered not on the number seven, but on the concept of “chunking” and our ability to memorize information accordingly. He found that the size of the chunks did not seem to matter — 7 individual letters could be as easily memorized in short-term memory as 7 individual words. While there are factors that influence how many chunks can be retained per individual (context, familiarity with content, specific capacity), the takeaway is the same: human short-term memory is limited and chunking helps us retain information more effectively.

When applied to UX design, chunking informs an incredibly valuable approach to content. When we chunk content in design, we are effectively making it easier to comprehend. Users can scan the content quickly, identify the information that aligns with their goal(s), and consume that information to achieve their goal(s). By structuring content into visually distinct groups with clear information hierarchy, we can align information with how people evaluate and process digital content. Next up, we’ll take a look at a few ways this can be achieved.

Examples

The simplest example of chunking can be found with how we format phone numbers. Without chunking, a phone number would be a long string of digits, which increases the difficulty to process and remember it. Alternatively, a phone number that has been formatted (chunked) becomes much easier to both process and memorize (Figure 4-1).

Figure 4-1. A (United States) phone number with chunking applied.

Let’s move on to a slightly more complex example. Browsing the Web will inevitably face one with the dreaded ‘wall of text’ (Figure 4-2). A ‘wall of text’ is content that’s characterized by a lack of hierarchy or formatting, and exceeds the appropriate length. It can be compared to the unformatted phone number example above but on a slightly larger scale. This content is more difficult to scan and process, which in effect will increase the cognitive load required from users.

Figure 4-2. ‘Wall of text’ example. (Source: Wikipedia)

When we compare the example above with content that has formatting, hierarchy and appropriate length applied, the contrast is significant. Below is an example of the improved version of the same content (Figure 4-3). Headings and subheadings have been applied to provide hierarchy, whitespace has been applied to break the content into discernable sections, line-length has been reduced to improve readability, text links have been underlined and keywords have been highlighted to provide contrast from the surrounding text.

Figure 4-3. ‘Wall of text’ improved with hierarchy, formatting and appropriate length. (Source: Wikipedia)

Now let’s take a look at how chunking is applied in the broader context. Chunking can be used to help users understand underlying relationships and hierarchy by grouping content into distinctive modules, leveraging rules to separate content, and providing hierarchy (Figure 4-4). Especially in information-dense experiences, chunking can be leveraged to provide structure to the content. Not only is the result more visually pleasing, but it’s more scannable. Users that are skimming the latest headlines to determine which is worthy of their attention can quickly scan the page and make a decision.

Figure 4-4. Example of chunking applied to dense information.

Key Takeaways

Don’t use the “magical number seven” to justify unnecessary design limitations.

Organize content into smaller chunks to help users process, understand, and memorize easily.

Remember that the short-term memory capacity will vary per individual.

Conclusion

The sheer amount of information around us is growing at an exponential rate. In contrast, we humans have a finite amount of mental resources to process the information around us. The inevitable overload that can occur directly has an affect on our ability to complete tasks. Miller’s Law teaches us to use chunking to organize content into smaller clusters to help users process, understand, and memorize easily.

Index

Miller, G. A. (1956). “The magical number seven, plus or minus two: Some limits on our capacity for processing information”. Psychological Review.