We all want higher customer loyalty, so knowing what “levers” move the loyalty-needle is important. If you can make changes that will increase loyalty, then increased revenue should follow. So, do improvements in usability increase customer loyalty?

To find out, Jeff Sauro took one of the more popular measures of perceived usability, the System Usability Scale (SUS) [PDF] and performed a regression analysis against Net Promoter scores. In total, he examined responses from 146 users from about a dozen products such as rental car companies, financial applications and websites like Amazon.com. The data come from both lab-based usability tests and surveys of recent product purchases where the same users answered both the SUS and Net Promoter question.

He found that the Net Promoter score and SUS have a strong positive correlation of .61, meaning SUS scores explain about 36% of the variability in Net Promoter Scores. The regression equation is:

NPS = 0.52 + 0.09(SUS)

So a SUS score of a 70 will generate an approximate Net Promoter Score of about a 7 and a SUS score of at least an 88 is needed to be a promoter (9+).

Does Better Usability Increase Customer Loyalty? Correlation Between the Net Promoter Score and the System Usability Scale (SUS)