Observe the behavioural tendencies of an 'isolated' individual, make note of the 'why'; why they choose to take action, what form these actions take, and study also their reactions to a given situation. Compare this then to their responses when said individual is placed amongst others; often pay witness to an almost entirely different person.
There is substantial evidence to support how an individual were to respond whilst witnessing a crime. For example, there is an identifiable correlation between the number of witnesses, and the likelihood of the observers in seizing the initiative to intervene within the prevention of said crime. The victim of an attack would do well, should there be less to witness the assault; for the assumption amongst the collective would be, 'surely another will intervene', a dangerous cogitation if this assumption is universally shared, and when time is 'of the essence'. Less witnesses, and the responsibility is more obvious, and noticeably dispersed amongst the few; a more compelling incentive perhaps, to take action.
Observable somatic 'symptoms' of an individual experiencing anxiety, can reveal the power of the internal, upon the external, and noticeable patterns can form within the likelihood of such reactions resulting, as can be identifiable. You would be right to fear those that are attuned to much of this; watch as thieves intentionally place signs within public spaces highlighting their presence, and witness the ease at which they steal from the people who react to said signs, as they reach for their items of value, and advertise where to target.