Usability, also known as ease of use, is defined according to the ISO 9241 standard as follows:
As the extent to which an interactive system, product or service can be used by specified users in a specified context of use to achieve specified goals effectively, efficiently and satisfactorily.
This means that a system is user-friendly if the user is able to fulfil his or her tasks with it completely and accurately, without interference, and has a positive attitude towards its use. It should also only use as many resources as necessary, but no more.
Usability can be measured on the basis of interaction principles (there are seven different ones: Task appropriateness, self-descriptiveness, expectation conformance, learnability, controllability, robustness against usage errors and user retention). These can be determined by a usability test or an expert review.

The user-friendliness of a system is tested by questioning potential users. Potential problems and weaknesses in the system can be identified through interaction with the website. Usability tests are now mainly carried out remotely, but are also possible on site and in test studios. Usability tests are referred to as Uselab.

There are basically two types of usability tests: thesis-generating tests are about gaining new insights and understanding about user behaviour and user-friendliness. This approach is exploratory; there are no predetermined expectations or hypotheses. The opposite happens with hypothesis-verifying tests, where predetermined hypotheses or assumptions about the usability of a product are tested.
The main advantage of a usability test is the direct feedback, which provides valuable insights into the needs and requirements of potential users.
Questions can be asked directly to the test subject in order to obtain even more precise information. The usability test is flexible in its implementation and can take place online or on site in a test studio.

Recruiting
When recruiting, the target group of the website should be taken into account. Depending on the duration of the test and the expected results, between 6 (for a protolab) and up to 24 (for a large usability test) volunteers are recruited. However, it is always advisable to over-recruit to allow for all eventualities.

It is important to find a representative group of people that reflects the usual users and their behaviour.

Research questions & implementation

Research questions are specific questions that serve to gather information and findings. They arise from the questions that concern the client and the information that they would like to obtain.
The interview guide is derived from the research questions and is used to systematically guide the participants through the test. The guide can now be used to collect specific information from the participants on the respective topics.
When the interview is conducted, the respondent is first explained how the test will be conducted. It is pointed out to them that they cannot make any mistakes, that the system is being tested and not they themselves. It is good if the respondent speaks out loud and shares their thoughts, known as thinking aloud. Finally, the respondent is asked for a general opinion, where they can once again comment on particularly positive or negative characteristics. It is important to ensure that the respondent is not asked any questions that would lead them too much and could influence their answer.

Final analysis and presentation of the results
Once the test has been completed, it is important to analyse the findings. This is where the transcripts of the interviews are reviewed and summarised. If not, it is crucial to find out what prevented it. The test subjects' outstanding behaviour and comments are analysed in order to identify patterns and establish cross-references between different participants. When analysing, the usage situation must be taken into particular consideration in order to determine the probability of occurrence and severity of the problem and to assign these problems to the corresponding interaction principles that were violated. Finally, the findings and possible solutions are presented to the client in a findings report, which can be followed by a workshop.

An expert review is a method that is separate from usability tests. Specialised usability experts take the time to take a closer look at the user-friendliness of a system. Two or more experts work independently of each other through pre-defined usage scenarios. They put themselves in the user's shoes and go through various steps to see how well or poorly the system works.
After they have completed their individual runs, they come together and share their findings. They discuss what went well and what didn't go so well. The aim is to filter out the strengths and weaknesses of the system and understand where there is potential for improvement.
An important step is then the evaluation based on the fundamental principles of usability. This means that the experts check whether the system is easy to understand, intuitive to use and error-resistant, for example. They ensure that it meets the needs and expectations of the users and supports them efficiently in their tasks.
Once all this has been done, the experts sit down together and brainstorm about possible improvements. They contribute their experience and expertise to develop concrete recommendations for action. These recommendations are aimed at making the system more user-friendly and effective.
Ultimately, the expert review is a clever way of finding out how good an online shop or app really is and how it can be made even better. It is like a kind of quality assurance that ensures that the needs of users are taken seriously and implemented.