Participants in an experiment are asked to look at pictures of different infants and rate the attractiveness of each infant on a 10-point scale. The participants are tested in groups of three and indicate their ratings aloud. For almost all of the infants, the participants tend to give ratings similar to other group members. We can be most certain that their ratings represent private conformity rather than public conformity if:

If they gave the same ratings alone as they do in a group.

Explanation:

The Conformity theory is referred to as a type of social influence that involves a change in belief or behaviour in order to fit in with a group.

This change can either be in response to real (involving the physical presence of others) or imagined (involving the pressure of social norms / expectations) group pressure.

Private conformity occurs when people truly believe that the group is right. They still believe the group is right even in the absence of group members.

While Public conformity occurs when we are pressured and feel we do not have a choice other than to conform or agree to group norms. This usually occurs before group members.

From the question context, if they gave the same ratings when they are alone and in a group, then we would say that private conformity has occurred.