In many cases, allegations of child abuse date back a number of years, making it difficult for victims to document precise times for the offenses. Some Canadian judges will allow the hearing of a case where the offense can be documented within 2 years of its occurrence, but other judges require that the time of the offense be determined within a range of 6 months. This seems unjust, since the fact that the offense occurred is all that must be proven. Another legal hurdle in child sexual abuse cases is the establishment of child victim/witnesses' legal competence to testify. Under Canadian law, persons 14 years old or older are presumed to be competent to testify. Witnesses under 14 years old are not presumed competent. Competence can be established if the child can be shown to understand the nature of an oath and the moral obligation to tell the truth. If the child is sworn, a conviction can be obtained on the child's evidence alone. If the child is not sworn, corroboration of the child's story is required. This involves the obtaining of evidence, independent of the child's statement, that the offense occurred and that the defendant committed it. If one material truth of the child's story can be corroborated, then other aspects of the child's story can be accepted by the court.