Measuring the cosmological density perturbation
  Precision measurements of anisotropies in the cosmic microwave background and of the clustering of large-scale structure have supposedly confirmed that the primordial density perturbation has a (nearly) scale-invariant spectrum. However this conclusion is based on assumptions about the world model and the nature of the dark matter. Physical models of inflation suggest that the spectrum may not in fact be scale-free, which would imply rather different cosmological parameters on the basis of the same observational data. 
Subir Sarkar (Oxford)