Detection of Usability Problems Depending on Sample Size

Moderated usability testing is the most frequently used method of usability assessment of digital interfaces since the appearance of this whole sphere in the late 20th century. The general purpose of this paper to create an accurate method to calculate sample size to such testing as there is usually used outdated model from the classic article written by Nielsen in 1993. The model was built using the results of 10 moderated usability testing provided by Russian company UsabilityLab. The resulting model will be compared with formula which was mentioned previously and models built later in. The goal was to clarify one of the variables of Nielsen's formula by adding 2 factors to it: experience level of participants and criticality of the problems which may be low, medium and high. This study can be matter of interest for those who use moderated testing as method of usability assessment.