Methods of pooling the standard deviation for a reference sample design. The standard deviation (σ) is pooled by taking the moving average of the variance(σ2). (a) Measured (σμ, gray) and pooled (σμ' (Imin), black) standard deviation of the difference of logged ratios μ, plotted against Imin. (b) Pooled standard deviation of MX, MY and μ plotted against the intensity metric used for pooling, Iavg or Imin. Data are from Dataset 5.