Answer-
Ed exhibited the most variable year to year performance over this 5 year span.
Solution-
Most variable performance means varying performance or non-consistence performance.
As shown in the graph,
Jill's performance was constant throughout 2005-07.
Ralph's performance was constant throughout 2006-07 and also in 2008-09.
Tina's performance was constant throughout 2007-09
Sam's performance was constant throughout 2008-09.
All of them has been consistence for at-least once. But, in case of Ed, throughout the time, his performance was in-consistence or variable.
