The correlation structure between power spectrum coefficients is complicated. Left panel: we plot the inverse of the Fisher matrix, i.e. the covariance matrix of the experiment. For illustrative purposes, we inverted the x and y axes. Right panel: patches around the diagonal elements of the normalized correlation matrix at low (ℓ = 200, upper row), intermediate (ℓ = 500, middle row), and high multipoles (ℓ = 800, lower row) reveal significant negative correlations between neighboring power spectrum coefficients at the 10% level.