  The purpose of this article is to carry out a power-spectrum analysis (based
on likelihood methods) of the Super-Kamiokande 5-day dataset that takes account
of the asymmetry in the error estimates. Whereas the likelihood analysis
involves a linear optimization procedure for symmetrical error estimates, it
involves a nonlinear optimization procedure for asymmetrical error estimates.
  We find that for most frequencies there is little difference between the
power spectra derived from analyses of symmetrized error estimates and from
asymmetrical error estimates. However, this proves not to be the case for the
principal peak in the power spectra, which is found at 9.43 yr-1. A likelihood
analysis which allows for a "floating offset" and takes account of the start
time and end time of each bin and of the flux estimate and the symmetrized
error estimate leads to a power of 11.24 for this peak. A Monte Carlo analysis
shows that there is a chance of only 1% of finding a peak this big or bigger in
the frequency band 1 - 36 yr-1 (the widest band that avoids artificial peaks).
On the other hand, an analysis that takes account of the error asymmetry leads
to a peak with power 13.24 at that frequency. A Monte Carlo analysis shows that
there is a chance of only 0.1% of finding a peak this big or bigger in that
frequency band 1 - 36 yr-1. From this perspective, power spectrum analysis that
takes account of asymmetry of the error estimates gives evidence for
variability that is significant at the 99.9% level.
  We comment briefly on an apparent discrepancy between power spectrum analyses
of the Super-Kamiokande and SNO solar neutrino experiments.
