Family first: Defining, constructing, and applying historical patent families

The article presents a novel method that enables the formation of historical patent families. Patent families are useful for studying the value of inventions and identifying key technologies, as they indicate geographic diffusion and higher patenting costs. The concept of patent family has not been employed in historical contexts as historical sources generally lack information about priority rights. The article provides a definition of a historical patent family, where patent families incorporate patents with the same invention core. The method is applied and evaluated by constructing Swedish patent families in 1885–1914 with historical patent data from Finland and the United States. Moreover, the article introduces the Patent Diffusion Index (PDI), which is an indicator of historical patent families which can be used to study the sequence and pace of market entry. The article exemplifies how historical patent families open novel perspectives on patent value and technology diffusion in contrast to current indicators, such as patent fees, which usually are bound to national contexts. The method is applicable to any national patent data, and patent drawings are suggested as an effective way to form historical patent families.