Dr. ratzinger has hypothesized that thimerosal vaccines cause autism spectrum disorder (asd). he compares a group of children who received the thimerosal vaccine and have been diagnosed with asd to a group of children who received the thimerosal but do not have a diagnosis of asd. the group of children with diagnosis of asd is referred to as the group; the group of children that does not have the diagnosis is referred to as the group.

Criterion and comparison.

Explanation:

Autism spectrum disorder may be defined as the developmental disorder that affects the behavior and communication of an individual. This disease can be diagnosed in the early stage of life.

Criterion group and comparison group both are involved in the discovery. Criterion group are used as a standard group in the research. The comparison group is used to compare the two different effects of the research.  Here, the children that receive thimerosal vaccine and diagnose with ASD are called criterion group beacuse this group helps to decide the effect of the drug. The group of children that receive thimerosal vaccine but do not diagnose with ASD are considered as comaprison group as they allow to compare the effects of drug.

Thus, the answer is criterion and comparison.