Levels of abstraction in students' understanding of the concept of algorithm : the qualitative perspective

In a former, mainly quantitative, study we defined four levels of abstraction in Computer Science students' thinking about the concept of algorithm. We constructed a list of questions about algorithms to measure the answering level as an indication for the thinking level. The answering level generally increased between successive year groups of Bachelor students as well as within year groups during the year, mainly from the second to the third level. The reliability of the instrument appeared to be good, but the validity remained unclear. In this current study, more qualitative methods are used to investigate the validity; the results indicate that the validity is good too. The study uses a theoretical perspective from Mathematics Education research and points at the fruitfulness of combining quantitative methods with qualitative methods.