Sesame Street is an American children's television program that is known for its use of format and structure to convey educational concepts to its preschool audience, and to help them prepare for school. It utilizes the conventions of television such as music, humor, sustained action, and a strong visual style, and combines Jim Henson's Muppets, animation, short films, humor, and cultural references. The show, which premiered in 1969, was the first to base its contents, format, and production values on laboratory and formative research. According to researchers, it was also the first to include a curriculum "detailed or stated in terms of measurable outcomes". The format of Sesame Street consisted of a combination of commercial television production elements and educational techniques. It was the first time a more realistic setting, an inner city street and neighborhood, was used for a children's program. At first, each episode was structured like a magazine, but in 1998, as a result of changes in their audience and its viewing habits, the producers researched the reasons for its lower ratings, and changed the show's structure to a more narrative format. The popular, fifteen-minute long segment, "Elmo's World", hosted by the Muppet Elmo, was added in 1998 to make the show more accessible to a younger audience. The producers of Sesame Street expanded the new format to the entire show in 2002. The format changed as the target audience did; by 2002 its main viewers were around two years old, while back in the 1960s the intended audiences were aged three through five. Original format The producers of Sesame Street, which premiered in 1969, used elements of commercial television such as music, humor, sustained action, and a strong visual style, in structuring the format of the show. They also used animation and live-action short films. The show's staff produced segments filmed in-studio with their human and Muppet cast and they contracted out the animations and short films to independent producers. Co-creator Joan Ganz Cooney was the first to suggest that they use commercial-like 12–90-second shorts that consistently repeated several key concepts throughout an episode. The studio segments were written to concentrate on the African-American child, a key component of the show's audience. The show's producers and writers decided to build the new show around a brownstone on an inner-city street, a choice writer Michael Davis called "unprecedented". They reproduced their viewers' neighborhoods—as writer Cary O'Dell described