Question: How long did the original broadcaster of the series that has the episode Known Unknowns, reign in the 18-49 Nielsen demographics?

<P0-S0> Season eleven, however, suffered a steep drop in ratings, a drop attributed by some to the arrival of new shows such as The Voice and The X-Factor. <P0-S1> The ratings for the first two episodes of season eleven fell 16–21% in overall viewer numbers and 24–27% in the 18/49 demo, while the season finale fell 27% in total viewer number and 30% in the 18-49 demo. <P0-S2> The average viewership for the season fell below 20 million viewers the first time since 2003, a drop of 23% in total viewers and 30% in the 18/49 demo. <P0-S3> For the first time in eight years, American Idol lost the leading position in both the total viewers number and the 18/49 demo, coming in second to NBC Sunday Night Football, although the strengths of Idol in its second year in the Wednesday-Thursday primetime slots helped Fox achieve the longest period of 18-49 demographic victory in the Nielsen ratings, standing at 8 straight years from 2004 to 2012. <SEP> <P1-S0> the loss of viewers continued into season 12, which saw the show hitting a number of series low in the 18-49 demo. <P1-S1> the finale had 7.2 million fewer viewers than the previous season, and saw a drop of 44% in the 18-49 demo. <P1-S2> the season viewers averaged at 13.3 million, a drop of 24% from the previous season. <P1-S3> the thirteenth season suffered a huge decline in the 18–49 demographic, a drop of 28% from the twelfth season, and american idol lost its top 10 position in the nielsen ratings by the end of the 2013–14 television season for the first time since its entry to the rankings in 2003 as a result, although the entire series to date had not yet been dropped from the nielsen top 30 rankings since its inception in 2002. <SEP> <P2-S0> "Known Unknowns" is the seventh episode of the sixth season of "House" and 117th overall. <P2-S1> It aired on November 9, 2009. <P2-S2> The team tries to diagnose a teenage girl while House is away at a medical conference with Wilson and Cuddy. <P2-S3> At the conference House finds something out about Cuddy. <SEP> <P3-S0> "House", also known as "House, M.D. <P3-S1> ", is an American medical drama series which premiered on Fox on November 16, 2004. <P3-S2> "House" was created by David Shore. <P3-S3> The show follows Dr. Gregory House (Hugh Laurie), an irascible, maverick medical genius who heads a team of diagnosticians at the fictional Princeton-Plainsboro Teaching Hospital (PPTH) in New Jersey. <P3-S4> In a typical episode, the team is presented with an unusual case; the storyline follows the diagnosis of the patient's illness, a process often complicated by the internal competition and personal foibles of the diagnostic team. <P3-S5> The team leader, House, frequently clashes with his boss (Dr. Lisa Cuddy (Lisa Edelstein) in seasons 1 through 7, and Dr. Eric Foreman in season 8), and his only friend, Dr. James Wilson (Robert Sean Leonard). <SEP> <P4-S0> realized for its gritty, realistic drama, st. elsewhere gained a small yet loyal following (the series did not rank higher than 49th place in the yearly nielsen ratings) over its six - season, 137 - episode run; the series also found a strong audience in nielsen's 18 -- 49 age demographic, a young demo later known for a young, affluent audience that tv advertisers were eager to reach. <P4-S1> the series also earned critical acclaim during its run, earning 13 emmy awards for its writing, acting, and directing. <P4-S2> st. elsewhere was ranked no. <P4-S3> 20 on tv guide's 2002 list of ``the 50 greatest tv shows of all time '', with the magazine also selecting it as the best drama series of the 1980s in a 1993 issue. <P4-S4> in 2013, tv guide ranked the series no. <P4-S5> 51 on its list of the 60 best series of all time.