**6. Discussion and conclusion**

In this study, three issues were tackled: investigation of the statistical nature of patent-paper citations, development of indicators, and tendencies of Japanese sectors' characteristics concerning patent-paper citations. Here, I discuss the findings and issues needed to be addressed:


and long-tailed nature of citations. If these indicators were used as monitoring tools, a long citation window would be a bottleneck for practical use. Exploring the possibilities of development of methods for shorter-time measurement and to show their availability and limitations should be an important theme.

**4.** HFPPCI might be inevitably sensitive to small changes in time sequence. Paper citation from high-feature-valued patents is a rarer phenomenon than that from all patents—even the latter is rare. Therefore, only a few citations might yield large changes to values of indicators. Chronological changes of HFPPCIs should be traced to grasp to what extent they are sensitive, and also possibilities for relaxing the threshold to increase samples should be addressed.
