Students who used the difficulty of exams as a basis for rating all other aspects of Professor Young's performance were probably influenced by

Horn's error

Explanation:

The Horn's error is related to the halo effect, it's a form of cognitive bias where someone uses a perspective to judge or conclude on a scenario. Where someone allows one trait, either good or bad, to judge a scenario. The students used the failure in this aspect, and it stands as the Horn's error or Halo effect.

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