Confidence intervals calculated with and without including the network structure. Distribution of Kendall's τ measuring the expected correlation between the expression levels of interacting proteins in S. cerevisiae. The grey distribution has been calculated under the correct empirical Null distribution, where pairs of interacting proteins are chosen such that the degree distribution of the re-sampled protein network is the same as that of the true network. The red bars indicate the distribution obtained under the conventional (and inadequate) Null model where pairs of proteins are chosen entirely at random. Including the network structure into the bootstrap procedure leads to a broader distribution.