  When analysing dark matter halos forming in cosmological N-body simulations
it is common practice to obtain the density profile utilizing spherical shells.
However, it is also known that the systems under investigation are far from
spherical symmetry and rather follow a triaxial mass distribution. In this
study we present an estimator for the error introduced by spherically averaging
an elliptical mass distribution. We systematically investigate the differences
arising when using a triaxial density profile under the assumption of spherical
symmetry. We show that the variance in the density can be as large as 50% in
the outer parts of dark matter halos for extreme (but still credible) axis
ratios of 0.55:0.67:1. The inner parts are less affected but still show a
scatter at the 16% level for these prolate systems. For more moderate
ellipticities, i.e. axis ratios of 0.73:0.87:1, the error is smaller but still
as large as 10-20% depending on distance. We further provide a simple formula
that allows to estimate this variance as a function of radius for arbitrary
axis ratios. We conclude that highly prolate and/or oblate systems are better
fit by analytical profiles that take into account the triaxial nature of
cosmological objects.
