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How to measure usability? (Part I)

Liisa Prits

There are various ways to measure usability. The most common methods include carrying out user surveys and/or polls, conducting user tests and measuring user statistics. Each method has its own important role and appropriate time in the process of measuring usability and product development as a whole. First of all, you should determine the purpose of measuring as it helps to choose the appropriate method or combination of methods.


What are usability metrics? 


Usability metrics are formulas based on statistical data that can help to evaluate how easy, quick and comfortable it is to use a particular web page or information system. Since metrics are primarily quantitative data, the results also provide a specific estimate that can be measured. Therefore, they are less subjective in comparison to qualitative data. Metrics can be used in measuring the usability of both simple web pages as well as more complicated information systems.


Why would you need to measure usability?


Metrics are useful because they let you regularly monitor the usability of your system, providing feedback about possible issues within the system. One of the main helpful factors of using metrics is having a consistent overview of user behaviour in the system. Thus, by employing metrics it is easy to determine which elements are difficult to use. In addition, metrics also provide information on the elements that are used more or less, the pages that get the most traffic, the time users spend on specific pages etc. There are many things that can be measured!


All of these metrics help to maintain and improve the usability of a system. Metrics can also be used for future progress as they help to plan subsequent development and design processes more easily. For instance, a particular metric may indicate that users are unable to find the right options from the menu.


Thus, you can now keep in mind that navigation should be simplified with the next system update. After a change has been made, however, you are able to observe the outcome—whether there are fewer errors now and whether usability has improved. Based on metrics, existing systems or functions can be also compared to their previous versions or even to other similar systems.


How to measure usability?


Usability is divided into several different measurable categories. Traditionally, there are five categories: the 5Es.


Effectiveness: How well and to what extent is the user able to achieve their tasks?

Efficiency: How quickly do users complete their tasks?

Engagingness: How well does the system engage users into using information? Are users engaged until the completion of the task? How satisfied is the user?

Error Tolerance: How well does the system prevent user errors and mistakes? How quickly do users recover from errors?

Ease of Learning: How easy is the system for first-time users? Does it get easier after repeated use?


This list is not set in stone and you do not have to feel restricted by the 5Es. Based on these traditional categories, every product owner may consult a usability specialist to determine the most suitable categories and the most useful metrics for their system. Other possible categories include: Memorability, Satisfaction, Preventing Information Overload, Preventing Errors, Purposefulness etc.


Each category is in turn divided into specific metrics. For instance, Effectiveness may measure the success rate of users completing their tasks. Efficiency may measure the time spent on completing the task. Error Tolerance may measure how many errors users make etc.


Usability score consists of the average percent rate of each category, while the average is in turn based on the average result of the metrics contained within it.


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