Abstract
The development of experimental competencies is an essential goal of science education, which also brings their diagnosis into focus. In general, hands-on competence tests are considered to be the most accurate way to assess experimental competencies. Thereby the competencies can be assessed using different methods of data collection, e.g. student protocols, video recordings during experimentation or interviews about the experiments. So far, there are no studies that systematically compare these methods and therefore allow to draw conclusions about the extent to which the method used influences the accuracy of the assessment result. However, such findings are crucial in order to be able to make a well-founded decision as to which method of data collection is sufficiently accurate and yet as economical as possible, depending on the context and goal of the assessment. The present study takes up this desideratum and examines exemplary competencies in scientific measurement of lower secondary school students: Based on student protocols as an economic way to assess competencies it was investigated to what extent the accuracy of the assessment result is increased by the addition of further methods. For this purpose, the assessment results were compared using student protocols, student protocols and videos, student protocols and interviews, as well as a combination of all three methods for 108 hands-on tasks about scientific measurement. The results show that the measurement competencies can be assessed much more accurately with additional interviews than without interviews. Furthermore, the results indicate that additional video recordings do not provide an advantage with regard to the accuracy of the assessment result, especially if additional interviews were conducted.