The corporation cited an increase in competition as a reason for the fall.
The report added: “Whilst 16-34s spent more media time with the BBC than with any other brand in 2019/20 and usage was within the target range, the amount of time spent was lower than the previous year given the increasing strength of competition, and was down proportionately more than older age groups.
“So, whilst the majority think that the BBC delivers the public purposes effectively, the scores that they gave in 2019/20 tended to be lower than those from over 55s across a range of measures.”
The BBC also said that eight in 10 children and young adults in the UK watch the BBC on average each week.
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