I often refer to an article by Nielsen Norman Group (N/N Group) on interaction cost. According to N/N Group the ideal interaction cost is zero.

Zero interaction cost is the Holy Grail. When the information a user needs is right in front of them, that equals zero interaction cost. The required effort it zero.

Reducing Interaction Costs

The interaction cost is the sum of efforts, mental and physical, that the users must deploy in interacting with a site in order to reach their goals”

To achieve a low interaction costs it is important to reduce the cognitive effort required from users. Zero interaction cost is rarely attainable. Most task need some level of cognitive effort. Whether clicking a link, scrolling down a page or scanning a page of text.

Below are a few of the factors that have a negative effect on interaction cost.

• Reading
• Scrolling
• Looking around to find relevant information
• Comprehending information presented to you
• Clicking or touching (without making mistakes)
• Typing
• Page loads and waiting times
• Attention switches
• Memory load; the information that users must remember to complete task

All the above increase cognitive load. To keep interaction cost low it’s important to reduce these factors in our designs.

Interaction Costs Applied

Levi’s have reduced interaction cost for the process of buying clothes online. They have acheived this by making options immediately visible on the page.

Most shopping sites hide options in dropdown menus. Compared to Levi’s solution this significantly increases the interaction cost. They need two or three clicks to achieve what is immediately visible on Levi’s.

On the Levi’s website with one click I can see if the colour of jeans I want are available in my size and length. No clicking or scrolling required.

Interaction Costs as a Measure of Usability

Interaction cost is generally a good measure of how difficult an interface will be to use for a user. So a large part of usability should deal with lowering interaction cost.

When accessing designs against each other compare the interaction cost of each. This will help you to understand which design is more likely to be successful.