A Kaiser Family Foundation study recently released concluded that live TV viewing by 8-to18 year-olds had declined by 25 minutes in the last five years - from three hours, four minutes in 2004 to two hours, 39 minutes in 2009.
"Our data which are based on observed behavior measured by digital meters, show that TV viewing for this group is actually up, not down as Kaiser found," according to Nielsen's Gary Holmes.
Kaiser's study was based on information recorded in diaries.
Nielsen has live viewing increasing seven minutes over the same period, from three hours and seven minutes in 2004 to three hours and fourteen minutes in 2009.
Kaiser notes that it seems to be the case that its study shows a bit more time-shifted viewing and less live viewing than Nielsen.