  When extracting cosmological information from power spectrum measurements, we
must consider the impact of super-sample density fluctuations whose wavelengths
are larger than the survey scale. These modes contribute to the mean density
fluctuation $\delta_b$ in the survey and change the power spectrum in the same
way as a change in the cosmological background. They can be simply included in
cosmological parameter estimation and forecasts by treating $\delta_b$ as an
additional cosmological parameter enabling efficient exploration of its impact.
To test this approach, we consider here an idealized measurement of the matter
power spectrum itself in the $\Lambda$CDM cosmology though our techniques can
readily be extended to more observationally relevant statistics or other
parameter spaces. Using sub-volumes of large-volume $N$-body simulations for
power spectra measured with respect to either the global or local mean density,
we verify that the minimum variance estimator of $\delta_b$ is both unbiased
and has the predicted variance. Parameter degeneracies arise since the response
of the matter power spectrum to $\delta_b$ and cosmological parameters share
similar properties in changing the growth of structure and dilating the scale
of features especially in the local case. For matter power spectrum
measurements, these degeneracies can lead in certain cases to substantial error
degradation and motivates future studies of specific cosmological observables
such as galaxy clustering and weak lensing statistics with these techniques.
