Music & Copyright has published new research separating out music retail sales by genre for the last ten years. Pop was the top genre, generating $7.4 billion of sales – a 29.2% market share. Rock wasn’t far behind with $6.5 billion of sales (25.7% share). Retail sales for the two genres fell over that decade 27.7% and 22.1% respectively, but both outperformed the overall music market, which fell 31% over the ten years. The big losers in that regard are Rap / Hip-hop, whose retail sales fell 48.3% over the decade, and Jazz, which fell 40.6%. Why the hip-hop decline? A variety of factors are suggested, including its large base of US sales, and public criticism of violent lyrics (although that’s by no means a 2000-2010 phenomenon).