Net Promoter Score (NPS)

In this article we will tell you more about the Net Promoter Score (NPS). We explain what the NPS means, how you calculate the score and explain how you can make it part of usability testing.

What is the Net Promoter Score?

The Net Promoter Score is a tool used to measure a company's customer loyalty - and is said to have a direct link to revenue growth and customer retention. The tool was developed in 2003 by Fred Reichmann and published in the Harvard Business Review. Its popularity has increased enormously ever since.

You measure the Net Promoter Score by asking customers one simple question:

How likely is it that you would recommend this company to friends and colleagues?

Depending on the answer given by the respondent, he can be classified in one of the following categories:

The critics (0 - 6) are people who have given a score of six or less. This group of customers is dissatisfied and can damage a company's reputation through negative word of mouth.

The passively satisfied (7 - 8) are people who have given a score of seven or eight. These are satisfied customers, but not necessarily enthusiastic about the delivered product or service. They are subject to competitor offers.

The promoters (9-10) are people who have given a score of nine or ten. They are loyal customers who are enthusiastic about the delivered product or service. They share their experience with other people and stimulate further growth of the company.

Calculating NPS

As with most quantitative usability metrics, you will have to have a rather large sample to draw any statisttical significant conclusions. To calculate the net promoter score of a group of people, you can use the formula below.

You always get a score between -100 and 100. Note that the net promoter score only has value when you can compare the score with companies from the same industry.

You can do this by looking at the average net promoter score within a specific sector. Some sectors, such as the energy sector, have on average always had a negative net promoter score.

NPS and usability testing

The use of the net promoter score in usability testing has a number of advantages:

• Easy data collection. Unlike other research methods, the NPS is very easy to plot and calculate.
• The net promoter score is known and loved by higher management. This is because the net promoter score has a strong correlation with turnover growth and customer retention.
• Strong correlation with the system usability scale, which means that the moment customers score high on the net promoter score (nine or ten), chances are that they experience your product as user-friendly.

The above points have ensured that the net promoter score has played an increasingly important role in UX research. For example, it can help to get buy-in from senior management to implement changes and provide an indication of the return achieved.

Side note to Net Promoter Score

While adding the NPS to usability testing can undoubtedly be of value, the following points should be taken into account:

1. Not an all-in-one usability metric

It is important to take into account that the NPS is not an all-in-one usability metric. We therefore recommend that you use it in combination with other metrics such as the task completion ratio and the time on tasks.

Apart from that, as is always the case with quantitative usability metrics, it does not provide any insight into the underlying motives of the respondent.

2. Beware of results that are not statistically significant

As with almost all other usability metrics, it is unlikely that you will receive statistically significant usability metrics with five usability tests. Depending on the size of the target group, you often need more response to get statistically significant results. It is therefore important to take this into account before you base rigorous design decisions on results that are statistically insignificant.

3. Difficult to measure progress

Because the net promoter score divides users into three groups: critics, passive satisfaction and promoters, it can be difficult to properly measure changes in the design.

For example, in the case where we score a predominantly 2 in an initial measurement and after an redesign we score an average of 6. From a UX point of view, the user experience has improved considerably, while according to the net promoter score the users are still critics.