Difficulty of using a product: subjective assessment

Subjective evaluation of a product's difficulty of use is part of a wider group of techniques known as subjective evaluation. These are concerned with the evaluation by one or more individuals of a set of variables. In the field of work activities, for example, the LOsange des Facteurs Humains (LOFH) is a technique of this type, which proposes to analyze a work situation using four grids [30].

Assessing the difficulty of using a product using a subjective approach consists in asking a user to appreciate the difficulty he or she feels when using a product. Etymologically, difficulty corresponds to the lack of ease felt by the user. This is the meaning we will use here.

Subjective assessment of the difficulty of using a product is one of the issues common to several disciplines. These include marketing, sociology, macro-ergonomics, psychology, physiology, ergonomics... [25]. The interest in this topic no doubt stems in part from the fact that a product may appear simple in appearance, but is ultimately complex to use. This type of observation, combined with major commercial failures, has had the effect of promoting the concept of simplicity of use in the industry. It should also be noted that a link can be proposed between the concept of difficulty of use and that of product complexity [29]. This new way of characterizing the complexity of a system by measuring its difficulty of use by an external actor provides a framework for better understanding G. J. Klir's famous phrase: "complexity is in the eye of the beholder"...

For the purposes of this article, we'll start with a review of the techniques most commonly used in marketing, sociology and macro-ergonomics. These allow a user to subjectively assess the "difficulty of use" of a product, among other characteristic variables. We will then examine other subjective evaluation techniques focused entirely on a product's "difficulty of use". These techniques come mainly from physiology, psychology and ergonomics. They are used to assess the "difficulty of use" of a product during predominantly physical or predominantly mental activities. The term "predominance" is deliberately introduced to emphasize the fact that the course of any activity always includes a physical component (motor action) and a mental component (information processing). Finally, this article will include a general discussion of the interests and limitations of the methods presented.