We are aware of the fact that the validity of this study has
some limitations. We identified and addressed the following
threats to its validity: (1) sample size – we engaged 5 users
as the usability tests show that 5 users reveal 75-90% of the
usability issues; (2) sample as a group of convenience – we
introduced the initial questionnaire and selected the sample
for UX evaluation to ensure its diversity; (3) confounding
variables – we performed the study in a strictly controlled
environment, where we limited the possible influences of
external factors; (4) subjective measurements – we
operationalized most of the variables to objective metrics,
the number of subjective self-reports is minimal; (5) small
number of gameplays – due to resource limitations in manual
measurements we focused on 2nd and 5th gameplay, which
were specified in the UX design goals.