One of the core indicators in the field of scientometrics is the number of papers published by a unit within a given period. However, such indicators can only be assessed properly by considering the unit's available resources. When evaluating the efficiency of institutions worldwide, the problem concerning the availability of internationally standardized data arises. While on the output side consistent publication indicators are available, these data are frequently not available on the input side. We therefore introduce a new input indicator reflecting the number of unique authors mentioned on the institutions’ papers. To demonstrate the new input indicator, we calculate efficiency scores for more than 3100 institutions from the higher education sector using output and the new indicator. It is the first time that an efficiency analysis is being performed for a multitude of institutions worldwide using a standardized input indicator. We present the results of two analyses: (1) Correlations of the new indicator with available staff numbers for institutions in single countries demonstrate that the numbers are closely related. (2) We utilize the standard data envelopment analysis (DEA) approach and variants. The DEA shows that the Harvard University is the best performing institution (in all years) followed by other institutions from Northern America or Europe. The institutional results correspond to what one knows from international university rankings. The results of both analyses reveal that the new input indicator based on co-authors is suitable for reflecting institutional staff numbers.