Professor Feldspar is upset. At the end of his three-year longitudinal study, he is positive that he did not disprove the Null Hypothesis. He is so despondent that he rushes out of his lab and ignores his graduate student, Suzy Schmidlap. Ms. Schmidlap took another look at the data and realizes that Professor Feldspar's work did yield a significant difference between groups.
Which type of error is Professor Feldspar guilty of?