Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
We present a model in which patent citations occur as new ideas are produced from combinations of existing ideas. An idea’s usability in this process is represented as an interval in a variety space of ideas, whose length determines the likelihood of citation. This process endogenously derives exponential aging of patents, which is consistent with empirical observations. The endogeneity of aging sets our process apart from the standard preferential attachment literature.