Figure 7
From: Addressing the Challenge of Defining Valid Proteomic Biomarkers and Classifiers
Effect of sample size on the determination of the distribution of standardized mean-differences. The distribution of a single peptide, ID:19655, was investigated for four different study designs (N = 7, 20, 33, 67) in 1000 re-sampled distributions out of the complete set of 134 cases and controls each. Typical effect size δ = (μmale - μfemale)/σ (with μmale and μfemalebeing the mean logarithmic intensity for a given peptide in the male and female population, and the pooled standard deviation) is shown. As is evident, studies of small sample sizes (e.g. N = 7) may determine the log change to be e.g. -5 or even +1, instead of the true change, which is about -2. The consequence of such an error, is that the data obtained from this small training set completely miss the correct effect size and cannot be generalized with even decent confidence.