Abstract
This paper explores the use of written tests and semi-structured interviews in ascertaining students' understanding of the concept of a variable. A written algebra test was administered to 379 students and from the results students were selected for a semi-structured interview. The types of questions asked and the medium in which they were asked appeared to influence the responses given. It is conjectured that these issues must be considered when endeavouring to reach a richer understanding of the students' perception of the concept of a variable.