Average View Duration

Because it is a length rather than a percentage, average view duration compares badly across videos of different runtimes. Four minutes is strong on a six-minute video and weak on a forty-minute one, which is why average percentage viewed sits beside it in Analytics. Use both. The percentage tells you how much of the video held, and the duration tells you how much of a viewer's evening you took. YouTube weighs retention against other videos of similar topic and length rather than against a universal number, so there is no target figure worth chasing. Chasing one tends to produce padded videos that hold nobody.