That there is no solid evidence of the effectiveness of such programs.
Explanation:
If your friend is thinking of purchasing a self-help weight-loss CD that promises its effects through subliminal persuasive messages embedded in the music, you should tell her that research shows that <em>there is no solid evidence of the effectiveness of such programs</em>. Subliminal messages are the ones that are not easily perceived, like images that are very quick to be perceived. Mass media usually uses these kinds of messages. At the time, there is no solid evidence to determine whether such programs are effective or not.
