“Analysis of the Use of Means-Plus-Function Claim Language in US Patents”

In December 2009, the United States Patent and Trademark Office (USPTO) issued over 16,000 utility patents. A recent analysis using a software program to tally those patents that include claims with means-plus-function (MPF) claim language revealed some interesting insights. The software searched for the terms “means for” or “means of” in the claims, and the results were quite revealing.

The analysis showed that only about 15% of the issued patents included at least one claim having an MPF limitation. Furthermore, of the patents that did include an MPF limitation, half recited fewer than five such limitations. This suggests that attorneys are primarily using MPF claim language as a back-up strategy, rather than a primary tool.

Interestingly, the study found that longer claim-sets are more likely to include means-plus-function language. Specifically, 21% of patents with above-average-sized claimsets (by character count) included a means-plus-function limitation, while only 11% of patents with below-average-sized claimsets included an MPF limitation.

On a claim-by-claim basis, the study found that only 3% of the patents in the sample included means-plus-function limitations in every independent claim. This further supports the notion that MPF claim language is not a primary tool used by patent attorneys.

The study also found a correlation between means-plus-function terms and non-assigned patents, which are usually filed by individual inventors. 23% of non-assigned patents included an MPF limitation, compared with 14% of assigned patents.

The data also revealed that patents arising from certain countries are much more likely to include MPF limitations. The most common foreign filing jurisdiction for priority claims was examined, and the percentage of US patents arising from those foreign filings that include MPF limitations was reported.

The use of means-plus-function claiming is primarily focused outside of the chemical and biotech art units. Only 2% of patents examined in TC1600 (Biotech & Organic Chemistry) and 7% of patents examined in TC1700 (Chemical & Materials Engineering) include MPF limitations. The remaining technology centers averaged over 18% of patents including MPF limitations.

The study also looked at the top-20 patent owners (based on the number of patents owned in the sample). These companies are all primarily focused on electronics and are all headquartered in either the US or East Asia.

The final part of the study showed the change in patent prosecution practice over time. Clearly, the use of means-plus-function claims has dropped over time. This is true even in the face of rising claim counts. The data was based on a sample of 22,000 randomly selected patents that issued between 1976 and 2009. The patents were grouped according to their decade of issuance and the percentage that included at least one means-plus-function limitation was calculated.

It is important to note that the search is likely both over and under inclusive. Although a claimed element that uses the terms “means for” is usually interpreted as an MPF claim, it is not always so interpreted. Likewise, claim terms written in functional language without any structure in the claims can be interpreted as means plus function even if the absence of the “means for” language. Also, “step for” language is typically when a method step is functionally claimed.

In conclusion, the study provides a comprehensive overview of the use of means-plus-function claim language in patents. It reveals that while the use of MPF claim language is not a primary tool used by patent attorneys, it is still a significant part of the patent prosecution process. The data also highlights the need for further research into the use of MPF claim language in different technology sectors and geographical regions.