Mass media effects increase when parental guidance is lacking. people cannot verify information through personal experience or knowledge. people have no prior information or attitude disposition regarding a subject. a specific medium has a greater reputation.

I believe the answer is: People cannot verify information through personal experience and knowledge
Due to inability to verify , People have no choice but to put a blind trust on the media that spread the information.
This would enhance the mass media effects where the media obtain a huge power to influence people's behavior and popular's opinion