Complex sentence: Ed Mintz founded CinemaScore in 1979 after "The Cheap Detective" disappointed his father, who wished he could have heard beforehand what "real people, not critics" thought of the film.
Split into simpler sentences: Ed Mintz founded CinemaScore in 1979 after "The Cheap Detective" disappointed him. According to his son, the elder Mintz wished he could have heard beforehand what "real people, not critics" thought of the film.