Asking someone what they think about other people reveals much about their own personality. The reason is that people tend to see more of their own qualities in others. The generous person sees others as generous and the selfish person sees others as selfish.
Dr Dustin Wood, the study's first author, said:
"A huge suite of negative personality traits are associated with viewing others negatively.The conclusions come from a series of three studies. In one people were asked to judge the positive and negative characteristics of three other people. The more positively they judged those people, the more happy, enthusiastic, capable and emotionally stable they turned out to be themselves.
The simple tendency to see people negatively indicates a greater likelihood of depression and various personality disorders."
Comment: Unfortunately, it's probably not as simple as the study predicts. Psychopaths are masters of deception who thrive in darkness. They might suss out the goal of the question and say what puts them in the best light. People with serious personality disorders cannot be counted on to have objective perceptions. There is also social programming to never say anything negative to contend with. Humans are much more complex than what can be revealed (or concealed) by a single question.