Subjective Measurement of Trust: Is It on the Level?

Psychometrics are increasingly being used to evaluate trust in the automation of safety-critical systems. There is no consensus on what the highest level of measurement is for psychometric trust. This is important as the level of measurement determines what mathematics and statistics can be meaningfully applied to ratings. In this work, we introduce a new method for determining what the maximum level of measurement is for psychometric ratings. We use this to assess the level of measurement of trust in automation using human ratings about the behavior of unmanned aerial systems performing search tasks. Results show that trust is best represented at an ordinal level and that it can be treated as interval in most situations. It is unlikely that trust in automation ratings are ratio. We discuss these results, their implications, and future research.