Doctor's degrees normally take four additional years of full-time study to complete. Requirements for obtaining a doctor's degree include taking additional advanced courses, passing an oral qualifying exam and submitting a longer doctoral dissertation which must represent a significant original contribution to knowledge in the field to which the dissertation topic is related. That contrasts with master's thesis, which, in addition to being usually shorter than doctoral dissertations, are not required to include creation of new knowledge or revision/reinterpretation of older views/theories. The doctoral dissertation is examined in a final oral exam before a panel of at least two members (in the state of São Paulo the preferred number is five, while the other regions prefer three members), usually including one or two external examiners from another university or research institute.