I really would be relieved if this were the figure - I would expect it to be considerably higher.
I asked a several groups of 13 year olds in a comprehensive about 12 years ago how many had seen such material (Papers submitted anonymously, of course) - and numbers were horrendous - back then!
Today, add peer pressure, natural curiosity and ease of access and I would be truly astonished if figures were under 80%.
It does not take too much for the age level to drop by a large margin.
I have been arguing this for a long time since having a major article published on this topic about five or six years ago.
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