A programme of post-first-degree or (post)graduate studies taken to gain doctorate.
The official higher education statistics record the number of students engaged in doctoral studies. This number of doctoral students underestimates the true number of postgraduates studying for a doctorate. The official statistics can only record those doctoral students who have enrolled at a university. However, many universities do not require students to be matriculated at a higher education institution while they write their doctoral thesis. Generally, such students are only required to matriculate for two semesters, which means that some of those studying for a doctorate are not recorded by the official statistics.
The examination statistics uniformly and largely completely record the number of those who successfully complete a doctorate. These results correspond to reality and are highly valid.
see: Types of studies