The bystander effect, or bystander apathy, is a social psychological phenomenon that refers to cases in which individuals do not offer any means of help to a victim when other people are present. The probability of help is inversely related to the number of bystanders. In other words, the greater the number of bystanders, the less likely it is that any one of them will help. Several variables help to explain why the bystander effect occurs. These variables include: ambiguity, cohesiveness and diffusion of responsibility.
http://en.wikipedia.org/wiki/Bystander_effect
Η ελληνική Βίκη το έχει αποδώσει επίδραση των παρευρισκομένων, κατά τη γνώμη μου λάθος. Η έννοια του effect εδώ είναι αυτή:
a scientific phenomenon: the Doppler effect.
http://www.thefreedictionary.com/effect
Φαινόμενο, δηλαδή, και όχι επίδραση. Το αποδίδω ως φαινόμενο της απάθειας των περαστικών. Τι λέτε κι εσείς;