This study investigated the use of performance-confidence relationships to signal the presence of alternative conceptions and inadequate problem-solving skills in mechanics. A group of 33 students entering physics at a South African university participated in the project. The test instrument consisted of 20 items derived from existing standardized tests from literature, each of which was followed by a self-reported measure of confidence of students in the correctness of their answers. Data collected for this study included students' responses to multiple-choice questions and open-ended explanations for their chosen answers. Fixed response physics and confidence data were logarithmically transformed according to the Rasch model to linear measures of performance and confidence. The free response explanations were carefully analysed for accuracy of conceptual understanding. Comparison of these results with raw score data and transformed measures of performance and confidence allowed a re-evaluation of the model developed by Hasan, Bagayoko and Kelley in 1999 for the detection of alternative conceptions in mechanics. Application of this model to raw score data leads to inaccurate conclusions. However, application of the Hasan hypothesis to transformed measures of performance and confidence resulted in the accurate identification of items plagued by alternative conceptions. This approach also holds promise for the differentiation between over-confidence due to alternative conceptions or due to inadequate problem-solving skills. It could become a valuable tool for instructional design in mechanics. IntroductionIn order to ensure a smooth transition between secondary and tertiary education, it is imperative for lecturers of physics to be well informed about the baseline knowledge and understanding of students upon entry to tertiary education. Furthermore, where lack of preparedness is identified lecturers should ideally be able to distinguish between a lack of knowledge about specific concepts and the presence of strong alternative conceptions. It is widely accepted that the instructional design for conceptual change of firmly rooted alternative conceptions will differ markedly from that aimed at acquisition of new knowledge or development of problem-solving skills. Hasan, Bagayoko, and Kelley (1999) proposed that a student's self-reported certainty of response could be used in conjunction with the answer to a conceptual test item to differentiate between lack of knowledge and the presence of misconceptions in mechanics. While acknowledging that their hypothesis is best utilised for individual students, they have expanded it for application to groups of students in an attempt to enable the lecturer to extract this information with relative ease for large groups of students. This paper investigated the use of the relationship between confidence and performance to signal not only the presence of alternative conceptions but also inadequate problem-solving skills in mechanics and as such serve as a practitioner's tool in ...