Dr. Carter has a reputation as a hard instructor and some students are warned about his Bio 260 class and fear it. On the other hand, some students taking his Bio 260 class have friends working in his lab and they have heard good things about Dr. Carter and are excited for the class. If at the end of the semester the first set of students give lower scores on teaching evaluations than the second ones, which cognitive bias is most likely responsible for this

The bias and anchoring is one in which previous information is assumed to be true by an individual who does not really know if that information is true. This makes this individual make decisions based on this information and keep those decisions for a long time, regardless of the impact it has. This can be seen in the case shown in the question above, where the students received the information that the teacher was a hard instructor and assumed that it would be very difficult to study with him, even without knowing if this information was true. This made the students decide to see the course as something very difficult, leading them to get low grades.