"FIMI: Certificazioni Archivio". FIMI. คลังข้อมูลเก่าเก็บจากแหล่งเดิมเมื่อ 2014-10-06. สืบค้นเมื่อ August 11, 2014. Note: To retrieve the certifications, 1) type in Katy Perry in the box of "Artista", 2) select "--" in the box of "Seleziona settimana e anno", 3) select "Album e Compilation" in the box of "Scegli la sezione" for albums or "Online" for singles, 4) click on "Avvia la Ricerca"
"IFPI Digital Music Report 2014"(PDF). International Federation of the Phonographic Industry. 18 March 2014. เก็บ(PDF)จากแหล่งเดิมเมื่อ March 18, 2014. สืบค้นเมื่อ 18 March 2014.
"FIMI: Certificazioni Archivio". FIMI. คลังข้อมูลเก่าเก็บจากแหล่งเดิมเมื่อ 2014-10-06. สืบค้นเมื่อ August 11, 2014. Note: To retrieve the certifications, 1) type in Katy Perry in the box of "Artista", 2) select "--" in the box of "Seleziona settimana e anno", 3) select "Album e Compilation" in the box of "Scegli la sezione" for albums or "Online" for singles, 4) click on "Avvia la Ricerca"
"Recording Industry in Numbers"(PDF). International Federation of the Phonographic Industry. 2013. คลังข้อมูลเก่าเก็บจากแหล่งเดิมเมื่อ 2013-04-09. สืบค้นเมื่อ March 2, 2015.{{cite news}}: CS1 maint: bot: original URL status unknown (ลิงก์)
"IFPI Digital Music Report 2014"(PDF). International Federation of the Phonographic Industry. 18 March 2014. เก็บ(PDF)จากแหล่งเดิมเมื่อ March 18, 2014. สืบค้นเมื่อ 18 March 2014.
worldcat.org
Harding, Cortney (September 13, 2009). "Katy Perry Kisses And Tells About Romancing Radio, Selling Songs And Getting Fans To Commit – To Her Album". Billboard. 145 (17): 34. ISSN0006-2510.