Abstract
While interdisciplinary research (IDR) has attracted much attention, this has not yet resulted in a coherent body of knowledge of interdisciplinarity. One of the impediments is a lack of consensus on its conceptualization and measurement. Some of the proposed measures have shown to misalign empirically, meaning that conclusions about IDR can differ across measures. To clarify this disagreement conceptually, and to stimulate better coherence in measurement, this paper starts with a review of the IDR definitions. From a synthesis of these definitions, we provide a conceptual definition and a logical structure of the construct, and derive evaluation criteria for its measures. We use these to evaluate 21 measures of IDR. The results show that measures vary widely in meeting the criteria, which can explain some of the observed inconsistencies in earlier studies. We discuss the most common limitations and present empirical analyses to gauge their severity. We present several suggestions for future measurement of the interdisciplinarity of research. We hope that with these suggestions, researchers can draw more consistent conclusions, aiding in the development of a coherent body of knowledge of this ever-important phenomenon.