  A principal component analysis of cosmic microwave background (CMB)
anisotropy measurements is used to investigate degeneracies among cosmological
parameters. The results show that a degeneracy with tensor modes -- the `tensor
degeneracy' -- dominates uncertainties in estimates of the baryon and cold dark
matter densities, omega_b = Omega_b h2, omega_c = \Omega_c h^2, from an
analysis of CMB anisotropies alone. The principal component analysis agrees
well with a maximum likelihood analysis of the observations, identifying the
main degeneracy directions and providing an impression of the effective
dimensionality of the parameter space.
