Final answer:
The bystander effect is best described as a diffusion of responsibility, where individuals in a group are less likely to act because they believe others will intervene.
Step-by-step explanation:
An aspect of the bystander effect best described by one of the options provided is the diffusion of responsibility. Specifically, this is when, in the presence of multiple bystanders, individuals assume someone else may be more qualified to intervene in an emergency or distress situation. Thus, they avoid acting themselves. According to the principles of the bystander effect, option 1) "When deciding whether or not to act, others look to see whether someone is more qualified, known as diffusion of responsibility." most accurately represents this psychological concept.