The Pareto principle states that a small part of the cause determines a large part of the effect. For example, 80 percent of the results can often be achieved with around 20 percent of the total effort. As a result, rapid progress can be made in many areas with a small number of actions, but this says little about the time required for full implementation.

Many projects have shown that you can make relatively fast progress at the beginning, because the tasks and their solutions are more or less thrown in your path and you don't have to search for them, so you can quickly reach 70-80% of the total project scope. The last 20 - 30 % of a project then takes much longer than the 70 - 80 % already achieved, because the remaining bugs and optimisations only become apparent after much searching and testing, and fixing them often creates other problems that none of the stakeholders had thought of before. This is why some projects drag on almost endlessly just before completion. This effect then leads to the fulfilment of Hofstadter's Law.

The Pareto principle has many applications. Mathematically, it is a simple power function that approaches an infinite maximum. Expressed as a percentage, it is 100%. Graphically, it is represented by a curve that rises very steeply at first, but then flattens out until it is almost horizontal.

Diagramm

This means that the Pareto principle can be applied not only to the 20/80 or 80/20 ratio, but also to the Pareto curve, which shows that, for example, 35% of the effort can achieve approx. 95% of the results or 10% of the effort can achieve approx. 50% of the results.

The 80/20 value pair is very intuitive and memorable and is therefore often used as a heuristic.

  • Pareto, V. (1906). Manual of Political Economy.
  • Juran, J. M. (1951). Quality Control Handbook.

Application in UX and UI design

The Pareto principle is widely used in both scientific studies and market research. Jakob Nielsen, a renowned expert in the field of UX and user research, has found in his studies that a increase in the number of test subjects rarely leads to new insights. This is because, due to the similarities between test subjects, almost every specific circumstance has already been covered in the course of the research, and new test results only confirm what has already been determined.

This principle is also applied to the projection of election results. Even counting a small percentage of the votes will often yield a result that differs from the final outcome by only a few percentage points.

In the area of usability studies, Nielsen has found that with as few as five test subjects, most (up to 85% or more) of the problems are identified, and with eight or more test subjects, virtually no new insights are gained. Therefore, for economic reasons, it makes sense to keep the number of participants small in this area.

A similar approach can be taken when testing the accessibility of a website. As a rule, all serious impairments can be found by examining 5-8 representative pages of different types, even if the website consists of more than 1000 individual pages. This is because most functionality is usually represented by about 4-6 page types or key templates.

Impact on the User Experience

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Further information