An in-depth study by lewis and colleagues of 12 convicted murderers diagnosed with dissociative identity disorder looked into their backgrounds. the study found strong evidence that each was severely abused, both physically and sexually. why does the text refer to this study as "flawed."

The study by Lewis et. al is considered to be "flawed" because the accounts of abuse in childhood are retold or recounted by the patient when they are adults. There is not enough "objective verification" and in some accounts there is no record or "outside verification" by others that the abuse even occurred.