Dr. Delgado is working on understanding aggression in children. Dr. Delgado and his associates stand outside a one-way mirror and note aggressive actions the children make after watching 15 minutes of violent videos. "Aggressive acts” were not clearly defined by Dr. Delgado and they found that many of the children's actions were not consistently rated between the observers. This is an example of poor:

a. Test-Retest reliability
b. Face Validity
c. Internal validity
d. Inter-rater reliability