Some scholars have argued that the possession of child pornography is immoral because it would validate the act of child sexual abuse or actively encourage people to engage in child molestation. In a 1984 study involving 51 child sexual abusers, 67% of the sample reported making use of "hardcore sexual stimuli". However, the study failed to prove that there was a causal relationship between such type of pornography usage and child sexual abuse.[citation needed] Other similar studies have also found a correlation between child molestation and usage of extreme erotic materials, but they did not limit the definition of "pornography" or "hardcore sexual stimuli" to child pornography.[66]