80 / 20 Rule

The pareto principal stipulates that 80% of outputs in a complex system are caused by 20% of total inputs. Explained simply, a large percentage of outcomes are caused by a small percentage of inputs (the actual numbers are not always 80/20.) What does this mean for web design? Lots of things.

For one a low percentage of users will perform a high percentage of your desired actions. For example 20% of all users will make up 80% of your contact form submissions or online purchases. 80% of users selecting from a drop down field will select the same 20% of options.

Once you know this disparity exists you can identify places to take advantage of it. The simplest implementation would be to prioritize the 20% of options, be them form fields, pages, links, etc… that get the most activity. Thinking broader, if you can learn about the 20% of high value users you can better optimize your design (and marketing efforts) to support their needs, increasing the amount of conversions you get from the site.

This principle says that 80% of the outcome come from 20% of the cause. When this is used in product design, it means that the unused functions or features could be removed due to the fact that they do not contribute to the outcome. This is similar to Ockham’s Razor as both principles suggest the same — the simpler, the better.