Forbes released their annual Celebrity 100 list earlier this week, and it's reason enough for Rihanna's frequent exhaustion spells. The "Where Have You Been" singer clocked in at No. 4, three spots behind the No. 1 seeded Jennifer Lopez.

Beyonce -- the current "Most Beautiful Woman" -- is considered to be the 16th most powerful celebrity, behind Taylor Swift, Britney Spears, Katy Perry and Lady Gaga. Dr. Dre led the way for rappers on the list, landing at No. 26, ahead of Jay-Z (No. 38), Diddy (No. 42), Kanye West (No. 45) and Lil Wayne (No. 69).

Unlike other Forbes lists -- i.e. "400 Richest Americans and World's Billionaires" -- that strictly tally net worth and money, the Celeb 100 measures earnings and the not-so tangible nor calculator-friendly property that is fame.

"We define fame as media visibility in print, television, radio and online, plus social media power, which we measure by looking at each celebrity's presence on Facebook and Twitter," the article explains. Forbes also cites cover spreads as "an important part of our fame algorithm." The list was compiled for the period between May 1, 2011, and May 1, 2012.

When it comes to hip-hop alone, the list is a head-scratcher. Dr. Dre, now a minority owner of Beats By Dre, reportedly earned $110 million in 2011, but only made two live appearances within the last year, both at Coachella. He has yet to put out his long-awaited Detox album. Not a major player on the Twitter medium, he can only boast 430K followers.

Meanwhile, Jay-Z and West put out one of the most successful and critically-lauded rap albums of 2011, Watch the Throne, and toured to sold out venues behind it. @kanyewest has more than 7.4 million Twitter followers and the 'All of the Lights' rapper's tweets are often news stories in and of themselves.

There are other questionable discrepancies as well, but endorsement deals and an already well-established fanbase might come into play here.

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