Ever major player in the record industry wants to know what makes a hit song a hit. However, researchers at the USC Marshall School Business and the USC Thornton School of Music, could now have an answer: back-up singers.

The research team looked at over 1,000 songs that went to number one on the Billboard Hot 100 list from 1958 through 2012, as well as over 1,400 songs that never made it to number 90. They listened to audio recordings of each song available, a total of over 2,000, with the help of graduate students. They analyzed each songs' instrumentation and vocals to come up with their results.

So what did the hit songs have that the others didn't? Researchers discovered that every hit song they listened to had back-up singers. However, songs that didn't make it past number 90 on the charts did not have back-up vocalists.

An award-winning 2013 documentary called 20 Feet From Stardom shined a light on back-up vocalists, who often go without receiving credit for their work. However, this new study shows that their involvement with a song could help it achieve success for its artist and that they can make or break a song.

So what else do hit songs have that make them so special? Researchers found that the use of synthesizer and guitars were also present on a lot of the hit tracks. In comparison, those tracks that did poorly on the charts featured acoustic guitar, acoustic piano and no strings; clean guitar and acoustic piano; or bass guitar, synthesizer and no electric piano.

The research team also found that hit song status was also affected by the number of instruments in the song.

"Our results suggest songs that do not follow conventional instrumentation have the best chance of becoming No. 1 hits," says Joseph Nunes, professor of marketing at the USC Marshall School of Business. "The average song has three to five instruments, but songs that feature a surprisingly low or high number of instruments— at specific points in time-tended to stand out."

However, the researchers pointed out that music is art, which means it's not always scientific.

"There are always exceptions and reasons other than the choice and number of instruments for a song's popularity," says Nunes. "For example, the star power of Rihanna may overcome any effect of instrumentation."

Those in the music industry, though, still might want to take note. If you want that next single to soar to number one, fire up the guitars and synthesizers and hire some back-up vocalists.