2.2 Usability

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2.2 Usability

2.2.1 Terms

The German language contains a number of words which are used synonymously with the term Usability, such as: Bedienbarkeit, Bedienerfreundlichkeit, Benutzbarkeit, Benutzerfreundlichkeit, Ergonomie, Gebrauchstauglichkeit, Handhabbarkeit, Nutzungsqualit�t, Software-Ergonomie, User Experience etc. However, the term Gebrauchstauglichkeit has established itself as the widely accepted translation of the term Usability. In this sense, the word »Gebrauch« refers to the context in which a product is used. In contrast to some of the above-mentioned terms (e.g. Benutzerfreundlichkeit) this term takes into account not only the user, but also the task to be completed. If the product does not support the user in completing a task, it is considered ineffective [FIT 2005][R�meling 2003].

The term Usability was initially defined in 1998 as part of the international standard ISO 9241-11; one year later it was translated into German [FIT 2005]:

English: »Usability«

(ISO 9241-11:1998)

»Extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.«

German: »Gebrauchstauglichkeit«

(DIN EN ISO 9241-11:1999; German Translation)

»Das Ausma� in dem ein Produkt durch bestimmte Benutzer in einem bestimmten Nutzungskontext genutzt werden kann, um bestimmte Ziele effektiv, effizient und zufriedenstellend zu erreichen.«

Jakob Nielsen, who is considered one of the leading authorities in the software and web design usability field, describes usability as the »degree of quality with which a user experiences an interaction« [Rampl].

In this thesis the term Usability will be used synonymously with the German terms Gebrauchstauglichkeit and Benutzbarkeit.

2.2.2 Measurability

The usability of a product can be measured using the ISO attributes of Effectiveness, Efficiency and Satisfaction. At the same time, these characteristics are unlikely to serve as a consistent standard as their significance will greatly depend on the user context and ultimate use objective. As a result usability should always be viewed in the context of its objectives. [R�meling 2003]. Given a user's different needs along with his/her subjective impressions, a purely objective assessment of usability is almost impossible.

Jakob Nielsen divides the concept of usability into five measurable factors, and also illustrates the diverse nature of the term usability with an interactive application system [R�meling 2003][van der Vlugt u. Stanley 2005]:

• Learnability: The user should be able to learn the system easily in order to complete his/her tasks.
• Efficiency: The user should be able to perform tasks quickly, thereby increasing productivity.
• Memorability: The user should be able to quickly re-establish proficiency in the operation of the system after a (prolonged) absence.
• Errors: The system should enable the user to have a very low error rate.
• Satisfaction: The operation of the system should be pleasant for the user.

Along these lines usability is seen as a measure of the quality of user-system interaction. It greatly influences the user's acceptance and accordingly, the success of a system.

2.2 Usability

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