The greater the number of other people present, the smaller in each individual's personal obligation to intervene. This statement best describes bystander effect.
Explanation:
The bystander effect is a psychological effect which restricts the mindset of individuals to help victim when the victim gets victimised in presence of large amount of people.
In this mindset, an individual will think the other person will go forward to help the victim and some individual may also have mindset to not to come in the forefront.
The factors like ambiguity, inability to express oneself in presence of group, group cohesiveness which means same as diffusion of responsibility. The individual will feel less personal obligation to intervene the unfair thing acting upon the victim.