In a child sex case decided under pre-amended R. 702, the trial court did not abuse its discretion by admitting expert opinion that the victim suffered from post-traumatic stress disorder when a licensed clinical social worker was tendered as an expert in social work and routinely made mental health diagnoses of sexual assault victims. The court went on to note that when an expert testifies the victim is suffering from PTSD, the testimony must be limited to corroboration and may not be admitted as substantive evidence.