Magic number 7+-2
The Magic Number 7±2 cognitive bias refers to the idea that the average human's working memory can hold around seven items (plus or minus two). This concept originates from a famous paper by psychologist George A. Miller in 1956, suggesting the limitations of human cognitive capacity, particularly regarding processing and remembering information.
How it works
Working memory is the part of short-term memory responsible for temporarily holding and manipulating information. The Magic Number 7±2 implies that when people attempt to retain information beyond this range, they start losing parts of it. The theory posits that our cognitive processing capabilities facilitate the grouping, or 'chunking,' of information into smaller, more memorable sets.
Examples
For instance, when trying to remember a phone number, individuals often divide the sequence into smaller groups (e.g., '123-456-7890' rather than a continuous string). Similarly, in grocery shopping, instead of recalling each item individually, people might categorize them into sections like 'fruits' or 'dairy products'.
Consequences
This cognitive limitation affects various areas where individuals need to recall complex information, such as multitasking or learning. It impacts decision-making processes, where people might oversimplify their choices due to memory constraints, leading to biases in judgments and inefficiencies in information processing.
Counteracting
To mitigate this bias, techniques such as chunking information and utilizing mnemonic devices can help increase memory retention. Also, using external aids like notes, lists, or digital tools to offload the cognitive load improves accurate information handling. Training and cognitive exercises can also expand working memory capacity.
Critiques
Some critics argue that Miller's original paper overstates the universality of this cognitive limit, noting exceptions and varying results across different population groups and settings. Furthermore, individual differences, such as expertise or familiarity with the information, can alter one's memory capacity.
Fields of Impact
Also known as
Relevant Research
The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information
Miller, G. A. (1956)
Psychological Review, 63, 81-97
51-57
Cowan, N. (2010). The magical mystery four: How is working memory capacity limited, and why? Current Directions in Psychological Science, 19 (1)
829-839
Baddeley, A. (2003). Working memory: looking back and looking forward. Nature Reviews Neuroscience, 4 (10)
Case Studies
Real-world examples showing how Magic number 7+-2 manifests in practice
Context
A 600-bed urban hospital replaced an aging electronic health record (EHR) module for inpatient medication ordering to streamline workflows and support more clinical decision support. Product managers and clinicians pushed to surface 'all useful choices' on a single ordering panel to reduce clicks and support diverse prescribing patterns.
Situation
The new order panel presented a single-screen list of 12 commonly used dosing regimens, 10 route options, and 8 frequency presets for each medication — all visible at once. Clinicians were expected to scan, select, and confirm without additional filtering or progressive disclosure during busy shifts.
The Bias in Action
Designers implicitly assumed clinicians could efficiently process the long list of options, underestimating working-memory limits described by Miller's '7±2' observation. As a result, clinicians experienced choice overload: they either scanned superficially and picked the first plausible option or spent extra time searching for the correct one. The increased in-the-moment cognitive load led to more selection mistakes (wrong route or frequency) and more frequent use of workarounds such as copying previous orders rather than using the panel.
Outcome
Within three months of deployment, medication selection errors reported in the voluntary incident system rose. Staff reported slower ordering times and greater frustration, and the hospital reverted to interim templates while redesign work began.