  Trust in human-robot interactions (HRI) is measured in two main ways: through
subjective questionnaires and through behavioral tasks. To optimize
measurements of trust through questionnaires, the field of HRI faces two
challenges: the development of standardized measures that apply to a variety of
robots with different capabilities, and the exploration of social and
relational dimensions of trust in robots (e.g., benevolence). In this paper we
look at how different trust questionnaires fare given these challenges that
pull in different directions (being general vs. being exploratory) by studying
whether people think the items in these questionnaires are applicable to
different kinds of robots and interactions. In Study 1 we show that after being
presented with a robot (non-humanoid) and an interaction scenario (fire
evacuation), participants rated multiple questionnaire items such as "This
robot is principled" as "Non-applicable to robots in general" or
"Non-applicable to this robot". In Study 2 we show that the frequency of these
ratings change (indeed, even for items rated as N/A to robots in general) when
a new scenario is presented (game playing with a humanoid robot). Finally,
while overall trust scores remained robust to N/A ratings, our results revealed
potential fallacies in the way these scores are commonly interpreted. We
conclude with recommendations for the development, use and results-reporting of
trust questionnaires for future studies, as well as theoretical implications
for the field of HRI.
