All artists included on this list, which have begun charting on official albums or singles charts have their available claimed figures supported by at least 20% in certified units. That is why Cliff Richard, Diana Ross, Scorpions, Bing Crosby, Gloria Estefan, Deep Purple, Iron Maiden, Tom Jones, The Jackson 5, Dionne Warwick, the Spice Girls, Dolly Parton, Ozzy Osbourne, Andrea Bocelli and others have not been included on this list. The more recent the artist, the higher the required percentage of certified units, this is because more music markets instituted certification systems after 1980s and 1990s.[a] So artists such as Rihanna, Chris Brown, Taylor Swift, Flo Rida, Katy Perry, Justin Bieber, Adele, Lady Gaga, Bruno Mars, Nicki Minaj and Ed Sheeran are expected to have their claimed figures supported by over 75% in certified units. The certified units are sourced from available online databases of local music industry associations. All certified units are converted from Gold/Platinum/Diamond certification awards based on criteria provided by certifying bodies. The certified units percentage varies according to the first year that an artist appeared in the charts.[b]
The requirements of certified units are designed to avoid inflated sales figures, which are frequently practiced by record companies for promotional purposes. The claimed figures are referenced from online articles created by highly reliable sources. For clarity, the sources used, say the term "records" (singles, albums, videos) and not "albums". However, if all available sources for an artist or band say "albums", such sources are only used if the certified album units of the said artist meet the required percentage amount. This list uses claimed figures that are closest to artists' available certified units: inflated claimed figures that meet the required certified units amount but are unrealistically high, are not used.
The claimed figures are upgraded only when there is a significant progress in artists' certified units. In other words, the available certified units for each artist should get relatively closer to already listed claimed figure in order for higher figures to replace the listed ones.
The certified units of the newer artists may sometimes be higher than their listed claimed figures. This is because Recording Industry Association of America (RIAA) and almost all other certifying bodies count streaming towards Gold and Platinum thresholds required for Digital Single Award certification. For this reason, some singles and even albums get over certified by hundreds of thousands of units. The over certified figures, however, are often in millions of units for RIAA certifications, one such example is Rihanna's single "We Found Love", which is certified at nine times Platinum by the RIAA, yet during the time of the certification, it had sold 5.4 million downloads.
The certified units for some artists/bands who have multi-disc albums can be higher than their listed claimed figures due to Recording Industry Association of America (RIAA) counting each unit within set as one unit toward certification.
Issued certifications for songs which have been recorded by multiple artists including featured artists are added to each artist's total amount of certified units, as all the artists would have played a significant part in a song. For example "This Is What You Came For" and "Where Them Girls At" include Rihanna and Flo Rida, Nicki Minaj as featured artists respectively, so the certifications issued for these songs are added to the total amount of certified units for all involved artists. However, the certifications issued for songs that have been recorded by four or more artists are not included as the artists involved would have played minor roles, examples of such songs are Kanye West's "Monster" and/or "All Day".[c]