  There have been conflicting claims as to whether or not power-spectrum
analysis of the Super-Kamiokande solar neutrino data yields evidence of
variability. Comparison of these claims is complicated by the fact that the
relevant articles may use different datasets, different methods of analysis,
and different procedures for significance estimation. The purpose of this
article is to clarify the role of power spectrum analysis. To this end, we
analyze only the Super-Kamiokande 5-day dataset, and we use a standard
procedure for significance estimation proposed by the Super-Kamiokande
collaboration. We then analyze this dataset, with this method of significance
estimation, using six methods of power spectrum analysis. We find that the
significance of the principal peak in the power spectrum (that at 9.43 yr-1with
a depth of modulation of 7%) shows a clear correlation with the amount and
relevance of the information being processed, as would be expected if there
were a real signal in the data. The significance level reaches 99.3% for one
method of analysis. We discuss, in terms of sub-dominant processes, possible
neutrino-physics interpretations of the apparent variability of the
Super-Kamiokande measurements, and we suggest steps that could be taken to
resolve the question of variability of the solar neutrino flux.
