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In a previous study of patent classifications in nine material technologiesfor photovoltaic cells, Leydesdorff et al. (2015) reported cyclical patterns inthe longitudinal development of Rao-Stirling diversity. We suggested that thesecyclical patterns can be used to indicate technological life-cycles. Upondecomposition, however, the cycles are exclusively due to increases anddecreases in the variety of the classifications, and not to disparity ortechnological distance, measured as (1 - cosine). A single frequency componentcan accordingly be shown in the periodogram. Furthermore, the cyclical patternsare associated with the numbers of inventors in the respective technologies.Sometimes increased variety leads to a boost in the number of inventors, but inearly phases--when the technology is still under constructio--it can also bethe other way round. Since the development of the cycles thus seems independentof technological distances among the patents, the visualization in terms ofpatent maps can be considered as addressing an analytically different set ofresearch questions.

Can Technology Life-Cycles Be Indicated by Diversity in Patent Classifications? The crucial role of variety