Some controversy over repression is that it touches on a very sensitive topic e.g. death, abuse etc. And asking people to take part in a study who have witnessed such events may be to much for them, so there is some ethical issues.
Evidence that supports repression is William's (1994) study of the role of repression. In between 1973 to June 1975 - 206 girls were admitted for sexual assaults. In 1994 20 years later, Williams studied 129 women who had been treated as a child aged 10 months to 12 years in a large city hospital. The interviews were conducted about 17 years later when all had reached adulthood. 16 women (12%) said that they had no memories of childhood sexual abuse; 38% said they did not recall the incident that brought them to the hospital. This study is often cited as proof that sexual abuse memories are often repressed, evidence for repression. Some criticisms of the experiment were: sexual abuse might have been suspected, but did not actually occur in some cases, some of the children brought to the hospital were under the age of 24 months, before the age when memories are retained; others were under the age of 36 months when memories are unreliable and frequently forgotten, the sample was biased as it mainly consisted of urban women, 86% of whom were African American and finally it was possible that the women did not want to tell the interviewers about the