Parkinson's Law
Work expands to fill the time available, which is why open-ended tasks in an interface tend to sprawl.
Definition
Cyril Northcote Parkinson's 1955 aphorism, published in The Economist, that work expands so as to fill the time available for its completion. In interface design it is used to argue for constraints, defaults and visible time expectations.
Craft convention. True because the industry converged on it. Breaking it costs familiarity, not correctness.
How it shows up in interfaces
A form with no indication of length invites hesitation. A meeting scheduler defaulting to sixty minutes produces sixty-minute meetings. A task list with no time estimates produces tasks that never close.
The design lever is the default and the visible expectation. Both set an anchor, and most users accept the anchor.
Applications
- Tell users how long a flow takes, and be accurate. 'Two minutes, four questions' outperforms an unlabelled form.
- Default meeting lengths to something shorter than the habit, such as twenty five or fifty minutes.
- Show step counts on multi-step flows so the end is visible from the start.
- Use time-boxed defaults in planning tools rather than open-ended fields.
In practice
Estimated completion time on forms
Surveys and applicationsStating an accurate time estimate up front raises completion. Stating an inaccurate one lowers trust and raises abandonment at the moment the estimate is exceeded.
Shortened default meeting durations
CalendarsCalendar products that default to twenty five and fifty minute meetings shifted a widespread organisational habit purely by changing a default value.
Sources
Where a source establishes something narrower than the popular reading of it, the note says so.
Parkinson's Law
C. N. Parkinson, The Economist, 1955
A satirical essay. Widely quoted, never experimentally established.
Procrastination, deadlines, and performance: self-control by precommitment
D. Ariely and K. Wertenbroch, Psychological Science, 2002
Experimental work on deadlines, and a better citation when evidence is required.
Continue from here
Each link says what the connection is, so you can tell a principle from an alternative from a thing people mix this up with.
Applies when you are designing
Why this works
The reasoning this entry rests on.
- Anchoring BiasCognitive bias
- Default EffectCognitive bias
Applied through
Where this shows up as a concrete interface decision.
- Progress IndicatorComponent
- MicrocopyUX writing
Related concept
Connected closely enough to change how you apply this.