Voyeurism 'under-researched' subject, says psychologist
14 April 2014 Last updated at 18:27 BST
The subject of voyeurism is under-researched as statistics are difficult to come by, a criminological psychologist has said.
In one Swedish study, around 11% of men have admitted to performing the act of voyeurism, Prof Anthony Beech of Birmingham University said.
He was speaking after 47-year-old teacher Gareth Williams from Cardiff pleaded guilty to charges of voyeurism after making recordings of children going to the toilet.
Williams also admitted making and possessing indecent images of children and will be sentenced next month.