Question about statement in paper

[rah37ds]

Hi, thanks for the paper and package. I really enjoyed reading the paper.
So this is more a question than an issue: in the paper you state "...Pearson and Spearman correlation are more noisy and cannot be used directly for the study of gene ex-pression relationships,.."
I wonder if you could elaborate on this and/or if you know some good papers or examples?

Thanks for your help!
Best,
Raph