What are claims in patent applications?
A patent application includes a ‘description’ and ‘claims’. The description discloses how the claimed inventions in the patent application can be carried out. They must be supported by or based on the description. Claims are important in the sense that their amount and content determine the scope of the patent rights. Scholars believe that the higher the number of claims in a patent, the greater the value or quality of the patent. Patent applicants also try to include many claims in their patent applications in order to protect their inventions more effectively.

What are the factors that affect the number of claims?
According to the IP5 Statistics Report 2017 Edition, the average number of claims per patent application was 14.7 at the European Patent Office (EPO), 10.4 at the Japan Patent Office (JPO), 11.2 at the Korean Intellectual Property Office (KIPO), 8.1 at the China National Intellectual Property Administration (CNIPA), and 17.6 at the United States Patent and Trademark Office (USPTO). If so, does this mean that the patent applications at the EPO on average are of better quality than those at the KIPO? What are the factors that can influence the number of claims in a patent application?

On the one hand, the expected market value of the inventions in a patent application can influence the number of claims. If the number of claims increases, the number of pages of the patent application and its complexity also increase. This may lead to higher costs for patent filing, such as patent attorney fees or patent office fees. Accordingly, applicants tend to ask patent attorneys to draft a higher number of claims only if their inventions have technological and economic value.

On the other hand, the fee system of a patent office can affect the number of claims. For example, in the EPO, filing fee and grant fee remain constant regardless of the number of claims, if it's no more than 15. (The filing fee for ‘EP direct-online’ with at most 15 claims is only 120 EUR regardless of the number of claims, but if it becomes 16, you must make an additional payment of 235 EUR.) Furthermore, the search fee, the examination fee, and the renewal fee remain constant, regardless of the number of claims. However, in the KIPO, most of the patent fees increase depending on the number of claims if it's more than just one. (The fee for request for examination is about 110 EUR(≒143,000 KRW) for a patent application with one claim, and you must make an additional payment of about 34 EUR(≒44,000 KRW) per claim.) This implies that the EPO incentivizes patent applicants and attorneys to write up to 15 claims, but the KIPO might mislead applicants into thinking that the number of claims should be as small as possible in terms of cost reduction, although the amount of payment is not substantial.

Implications
In conclusion, the patent fee systems of patent offices as well as the technological and economic value or quality of patents affect the number of claims in an individual patent application and the average number of claims across patent applications filed at a patent office. In addition, the following implications can be inferred:

1. The difference in average numbers of claims per patent application among patent offices is not only ascribed to the (average) value or quality of the patent but also to the differences in the patent fee system.
2. The comparison of the average number of claims by technology sector, firm or nationality in the same patent office can be more meaningful than the international comparison across several different patent offices in terms of the technological and economic value or quality of patents.
3. The patent fee system where the patent fees remain constant up until a certain number of claims (e.g. 15 or 20 claims) may enable applicants or patent attorneys to protect their inventions more effectively, as the number of claims will not be influenced by financial reasons.