princípio
Pareto principle
In many events, roughly 80% of the outcomes come from 20% of the causes.
Find the 20% that solve 80% and give them pride of place.
In 1896 Vilfredo Vilfredo ParetoObserved, studying land ownership in Italy, the unequal distribution that became the 80/20 principle.One reference in this work:1897Cours d’économie politiqueSee on Wikipedia ↗See in the bibliography → described a very lopsided income distribution in Italy, with a minority holding most of it, and the lopsided shape turned up in so many contexts that it became a rule of thumb. In product, it usually means that a minority of the features accounts for most of the real use. The practical value is not in the exact number, which varies, but in the question it forces you to ask about which paths almost everyone takes and whether they get attention in proportion to that. In most products they don’t, because effort tends to spread itself evenly.
Why there is no neuroscience here
The biological mechanism behind the effect, and how much of it was actually measured.
Pareto observed income distribution in Italy, and the regularity that bears his name is statistical: in many systems the distribution is skewed, and a minority of the causes accounts for most of the effects. It is not a law of nature and there is nothing neural about it, the exact proportion varies, and in many cases it is nothing like 80/20 at all. What makes it useful in product is verifiable and within your reach. The telemetry of your own system says which features carry the use, and your product’s number is worth more than the famous proportion.
Why this law presumes no body at all
Who it was measured on, and what changes when the body on the other side is another.
A few features concentrating almost all the use is a property of the set, not of who uses it. The trap lies in confusing the two. The 20% most used are not the 20% most critical, and what is rarely used may be precisely what saves someone on a bad day.
How design translates it
What to do with it on a screen, without turning a finding into a rule.
How to measure this in your product
Identifying the 20% that solve 80% of the interactions and giving them prominence, a shortcut and a place in the main menu makes the interface leaner and more focused: the initial effort drops and the sense of control rises. What says which ones those 20% are is the telemetry of your own product, not a hunch, and prioritisation frameworks such as the Kano model help separate, within them, what is basic from what delights.
Where it breaks
Where the law does not hold, holds less, or holds in reverse.
The 20% that solve 80% of the cases are not the 20% that are most critical. Frequency is not importance: the feature used once a year may be exactly the one the person subscribed for.
Um caso
A real product where this showed up, with what happened and where to check it.
Five commands in a third of Word
In 2006 Jensen Harris published the usage data for Word 2003, collected from those who agreed to take part in Microsoft’s telemetry. The five most used commands, Paste, Save, Copy, Undo and Bold, accounted for about 32% of all use, and Paste alone for more than 11%, twice the second. The data changed a decision. The team was considering removing the copy and paste buttons from the new interface, because everyone knew people used the keyboard shortcut, and the data showed that the Paste button was the most clicked of all. It became the first big button on the first tab. The same post records what the principle does not authorise. After the first ten commands the curve flattens, and the difference in use between the hundredth and the four-hundredth is similar to the difference between the first and the eleventh. People use a lot of the product’s breadth. Telemetry says what deserves prominence, and it does not authorise cutting the rest.
Experimente
A piece to check in your own body what the text has just claimed.
Which functions would you leave on the first screen
This is a bank’s menu, with the twenty functions ordered from most used to least used. Drag to choose how many would fit on the first screen and see how much of the use they cover and what is left out.
80% of use fits in 4 functions, the last one being Pay a bill slip. The first one that ends up behind “more” is Card: bill, and the whole tail adds up to 20%.
This curve is a model, and its shape shows up in real data: in Word 2003, the five most used commands added up to 32% of all use and Paste alone was over 11%, as the case below tells.
Who actually said this
The name the law carries, who actually wrote it, and why the mix-up stuck.
The 80/20 is not Pareto’s. It is Joseph JuranFormulated the rule of the “vital few”, christened it the Pareto principle and later published a retraction saying the name was wrong.One reference in this work:1975The non-Pareto principle: mea culpaSee in the bibliography →’s, 1940s.
Vilfredo Pareto described, in the Cours d’économie politique, a very unequal income distribution in Italy. He formulated no rule, never said 80/20 and did not suggest it held outside economics. The one who generalised it was Joseph Juran, a quality engineer, who found the same lopsided shape in factory defect counts and called it “the vital few and the trivial many”. When it came to naming the chart, he christened it the Pareto principle, and then spent the rest of his life trying to correct the attribution. In 1975 he published a retraction titled “The Non-Pareto Principle: Mea Culpa”, explaining that the idea was his and the name, borrowed.
JURAN, J. M. The non-Pareto principle: mea culpa. Quality Progress, v. 8, n. 5, p. 8-9, 1975. Source
Neighbouring concepts
Sibling concepts
Fontes
Enunciado citado de Pareto, 1896.
- PARETO, V. Cours d’économie politique. Lausanne: F. Rouge, 1896-1897. 2 v. Source
Leitura complementar: Pareto Principle Laws of UX em inglês