The Pareto Principle

Vilfredo Federic Damaso Pareto was born in 1848. During his notable career in the field of micro-economics, he observed that 80% of the income in 19th century Italy went to the richest 20% of the population. This became known as the Pareto prinicple, and later on as the more general “80/20 rule” As you can imagine, it’s a significant stretch to relate an observation about wealth distribution in Italy to the design of user interfaces, but it does happen. I have three main problems with Pareto being used to justify decisions…

1. The data rarely backs it up
   Even with tonnes of usage data, or Google Analytics data, it’s very tricky to find this mythical 20% that accounts for 80% of the usage. Also, if/when you do find it, you have to make sure that it reflects what the users want, not what they click. I’ve worked with clients who were adamant that their “About page” was their most popular, only to see all the users end up there whilst hunting for a non-existent contact number. Analytics only tells you the what, not the why.
2. Some vital features are rarely used
   From what I’ve seen, less than 1% of users will change their password arbitrarily. If you’re just going to focus on the 20%, you can annoy a lot of people. There are a lot of high priority features that don’t see much usage.
3. What does it really mean?
   If I told you that Paste, Save, Copy, Undo and Bold account for 32% of the commands used in Microsoft Word, would you really alter the UI based on that? Paste alone is responsible for 11% of the commands, so it should have a super big button, right? At least 25 times the size of word count? Nonsense.

I know we use Pareto’s principle as a little nugget to capture clients ears and make them think about focussing on what's important rather than expanding their product to become the sum of all desired features. That's understandable. But in this new age of Less Software(tm), lets not get carried away. You can’t design software based solely on quantitative research. Especially when that research comes from 19^th century Italian economics.