The last few years of the decade were dominated by Sia’s power pop. Sia Furler was a hired-gun songwriter who decided to stop letting vocalists like Rihanna and Beyonce have her best material, and ended up becoming a huge pop star herself. She dealt with the handicap of being over 40 by performing with her face covered. The paper-bag gimmick may seem extreme, or unnecessary, but it paid off, in part because it was new, and also because it put the focus back where it needed to be, on the singing. Sia has bigger lungs than just about anyone else out there. She can belt it out to the back rows of a football stadium and still make it sound like she’s crying in her bathroom. Being a generation older than most of her clients puts Sia ahead in at least one regard; she actually has something to write about, like a lifetime of ups and downs, failures, regrets, heartbreaks and breakthroughs, aka a lifetime of life lived that a girl of 20-something just doesn’t have to fall back on.