Question: How many people on average watched the first four seasons of Grey's Anatomy?
About the article "Grey's Anatomy", section "U.S. television ratings".

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Critics included "Grey's Anatomy" in top ten lists for four of its first six seasons; these are listed below in order of rank. 
"Greys Anatomy" has received high viewership and ratings since its debut.
The first four seasons of the program each ranked in the top ten among all viewers, reaching its peak Nielsen ratings in the second season, attracting an average of 19.44 million viewers per episode, and ranking at fifth place overall.
Following the show's time-slot being relocated, overall rankings steadily declined, dropping below the top ten in its fifth season.
"Grey's Anatomy" made its greatest fall from its sixth to seventh season, slipping from seventeenth place to thirty-first.
The series is on a steady decline in terms of overall viewership and rankings, yet "Grey's Anatomy" still holds value in charts when numbers are pulled from the digital video recorder (DVR).
It was the most recorded show between 2007 and 2011, based on cumulative totals, and has been for several years in a row.
The most-watched episode of the series is "It's the End of the World", with 37.88 million viewers, aided by a lead-in from Super Bowl XL.
In contrast, the least-watched episode is "The Lion Sleeps Tonight", which garnered 8.19 million viewers—a 30% decrease from "It's the End of the World".
In 2011, "Grey's Anatomy" was named the fourth-highest revenue earning show of the year, with US$2.67 million per half hour, behind "Desperate Housewives", "Two and a Half Men", and "American Idol" at the top.
In 2012, the show was the fifth-highest revenue earning show of the year, with US$2.75 million per half hour, behind "Glee", "Two and a Half Men", "The X Factor (U.S.)" and "American Idol".
While "Grey's Anatomy" is no longer ranked in the top numbers for overall ratings, the show's ranking in the key 18–49 demographic has remained high.
As of season eight, the series is the highest-rated drama on television in the target demographic.
Below is a table of "Grey's Anatomy"s seasonal rankings in the U.S. television market, based on average total viewers per episode.
Each U.S. network television season starts in September and ends in late May, which coincides with the completion of May sweeps.
The first episode was watched by 1.877 million viewers, an 8.8% audience share, ahead of the first episode of "Facejacker" (1.186m) on Channel 4, and an episode of "Grey's Anatomy" (0.853m) on Five. 
The fourth season of the American television medical drama "Grey's Anatomy", commenced airing in the United States on September 27, 2007 and concluded on May 22, 2008.
The season continues the story of a group of surgeons and their mentors in the fictional Seattle Grace Hospital, describing their professional lives and the way they affect the personal background of each character.
Season four had twelve series regulars with ten of them returning from the previous season, out of which eight are part of the original cast from the first season.
The season aired in the Thursday night timeslot at 9:00 EST.
In addition to the regular seventeen episodes, a clip-show narrated by the editors of "People" recapped previous events of the show and made the transition from "Grey's Anatomy" to "Private Practice", a spin-off focusing of Dr. Addison Montgomery and aired on September 19, 2007, before the season premiere.
The season was officially released on DVD as a five-disc boxset under the title of "Grey's Anatomy: Season Four – Expanded" on September 9, 2008 by Buena Vista Home Entertainment.
For the first time in the show's history, many cast changes occur, seeing the first departure of two main cast members.
The season received mixed response from critics and fans, resulting in several awards and nominations for the cast members and the production team.
Show creator Shonda Rhimes heavily contributed to the production of the season, writing five out of the seventeen episodes.
The highest-rated episode was the season premiere, which was watched by 20.93 million viewers.
The season was interrupted by the 2007–2008 Writers Guild of America strike, which resulted in the production of only seventeen episodes, instead of twenty-three originally planned. 
"The Story" is a song released as a single by American folk rock singer Brandi Carlile, written by Phil Hanseroth, from her 2007 album "The Story".
It was featured in "Grey's Anatomy" in 2007 and is on Grey's Anatomy Soundtrack album 3 (released September 11).
About four years later, a version of the song has been recorded by "Grey's Anatomy" actress Sara Ramirez and was first presented in the 2011 episode "Song Beneath the Song".