What is the best description for an event that increases the likelihood of a behaviour being repeated?

The best description for an event that increases the likelihood of a behavior being repeated is a reinforcer. Reinforcement, in the context of behavioral psychology, refers to any stimulus or event that strengthens or increases the probability of a specific response or behavior occurring again in the future. This can involve positive reinforcement, where a pleasant outcome or reward follows a behavior, or negative reinforcement, which involves the removal of an unfavorable condition following the behavior.

While punishers and neutral stimuli do play roles in behavior management, they do not promote the repetition of a behavior. Punishers decrease the likelihood of a behavior being repeated by introducing an unpleasant consequence or removing a pleasant one, and neutral stimuli do not have significant effects on behavior reinforcement or punishment. Negative vicarious reinforcement, in particular, refers to observing someone else experiencing a negative reinforcement and does not directly increase the likelihood of one's own behavior being repeated. Therefore, the correct answer emphasizes the fundamental role of reinforcement in strengthening behaviors.