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