  Azimuthal distributions of particles produced in nucleus-nucleus collisions
are measured with respect to an estimated reaction plane which, because of
finite multiplicity fluctuations, differs in general from the true reaction
plane. It follows that the measured distributions do not coincide with the true
ones. I propose a general method of reconstructing the Fourier coefficients of
the true azimuthal distributions from the measured ones. This analysis suggests
that the Fourier coefficients are the best observables to characterize
azimuthal anisotropies because, unlike other observables such as the in-plane
anisotropy ratio or the squeeze-out ratio, they can be reconstructed
accurately.
