Primacy Effect When people form opinions about a person or a situation, those opinions are likely to be based on first impressions, on an initial assessment of the person or situation. In other words, the opinions we have of people or situations tend to be based much more on the first information we learn about them than on information we learn later. This tendency is called the primacy effect. Researchers believe that the primacy effect occurs because after people have made an initial judgment, they tend to notice evidence that supports that judgment, and disregard or fail to notice evidence that contradicts it.