# Cumulative Impact of Testing Factors in Usability Tests for Human-Centered Web Design +
## 1 Introduction  
The paper is dedicated to exploring the combined impact of factors that affect the results of usability testing. Usability testing is a key procedure that allows for making sure that the quality of user interfaces is good enough; moreover, it allows for testing technical, structural, and aesthetic features of interfaces, including the latter for online media. A substantial number of studies of usability testing orients itself to the factors affecting usability and united under the umbrella of the so-called 'contextual fidelity' model [1, 2, 3]. The model includes the four factors such as the test conditions, participants' traits, properties of the tested product, and task features. Together, they form the conditions of usability testing that can significantly affect both the testing accuracy and the final result of the tests. Selection of these factors as the main overarching parameters influencing user experience and efficiency dates back to the 1970s, and they have been investigated in a large number of studies before being aggregated, recently enough, into one model that may be used for assessing their relative importance and cumulative impact upon usability of interfaces. However, today, most studies assess the influence of these factors, viewing them as separated from each other and not addressing their cumulative impact; this is why the 'contextual fidelity model' as such has not yet been in wide use, while the four factors were acknowledged as contextual and shaping DUXU experiments long ago. In the overwhelming majority of studies of user interfaces, various characteristics within individual factors are investigated [4; 5; 6]. Such studies focus on specific aspects of user behavior during the test [7], of testing tasks [8], of the tested product [9], or the test context [10]. Unfortunately, in most cases, they do not attempt to establish relationships between these factors; neither they assess whether the 'contextual fidelity' factors affect each other during test procedures. In particular, testing environment studies look at laboratory vs. field testing efficiency [11; 12], or, e.g., the impact of remote testing on the overall user experience [13]. Analogously, product-focused research unidirectionally examines the impact of usability upon objective user's cognitive productivity [14], as well as its influence upon subjective perception of quality, including perceived usability [1] and perceived aesthetics. As a rule, in most of such studies, the results test a direct relationship between individual parameters of subjective user evaluations of their experience and/or objective user performance, on one hand, and the aesthetic quality of web portals, on the other [15; 16], without assessment of possible other factors and/or their combinations that may shift the results within the experimental setting. Similarly, the influence of aesthetic quality of a website upon user experience has become a growing area of research--which, however, remains quite narrow in its scope and highly under-researched. In it, studies of combinations of aesthetic features, task qualities, and experimental conditions are almost non-existent. In particular, the effects of web aesthetics upon user experience and satisfaction can be divided into subjective and objective ones. Subjective effects are linked to changes in user perception of certain qualities of a product, due to the layout aesthetics. The most significant effects here emerge under the impact of the relationship between aesthetics and perceived usability, when, as experiments show, a product with higher aesthetic quality is also perceived as more convenient to use. The influence of product aesthetics upon objective criteria of usability and, in particular, upon cognitive performance, remains under-investigated, despite a number of important studies in this area. Here, a certain contradiction in the research results may be spotted.