American Idol might still be the No.1 show on TV, but the ratings continue to slip.

Wednesday’s Portland auditions episode had 18.19 million viewers and a 5.9 rating among adults 18-49. That’s down from last week and of course last year. Thursday’s show from St. Louis had 17.4 million total viewers, according to the Nielsen ratings system. That’s just about even with last week, but far less than last season.

For the third week in a row, American Idol was beaten Thursday in the important 18-49 age group by CBS’ “The Big Bang Theory.”

So what’s behind this season’s ratings? Music Editor for The Hollywood Reporter has an idea.

“Last year, they came out with such a bang,” said Shirley Halperin who also writes the Magazine’s ”Idol Worship” blog. “It was such a novelty to see Lopez and Tyler. They really upped their game in terms of celebrity quotient. This year feels kind of like the sophomore album. Everything seems a little ho-hum.”

Judge Randy Jackson want’s to point out an important factor.

“Idol’s in its 11th season, it’s still the number one show on television, not by the huge margins it was before,” Jackson told THR.

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