[en] Understanding the attrition among PhD candidates and modelling the mean or median time to degree according to certain factors have been at the center of the research interest in higher education for a long time. This paper presents a conceptual literature review divided into two parts.
First, the multitude of factors used to explain the doctoral outcome is presented and results concerning their impact are summarized. We also propose explanations for potentially controversial findings and advice on the proper use of these factors.
Then, an overview of the most common statistical techniques employed is displayed. The authors argue that some techniques are more adapted than others to deal with such data and the issues of interest and they give recommendations about the most appropriate techniques. They also highlight some of the key points that are essential to consider in order to conduct an adequate statistical analysis when dealing with PhD data.
An overall conclusion is that there is much variability in the factors and their definitions, the same comment holding for the techniques. This explains why studies end up with different (sometimes controversial) results.