The mean dilution effect. For each sample type, the mean percentage of Ki67-positive cells, over the 50 samples, is plotted against the number of cells counted. The dashed blue line corresponds to core biopsies and the dashed yellow line to surgical specimens. The shaded areas represent pointwise 95% confidence intervals for the means. The confidence bands are overlapping. Therefore, an intermediate grayscale was used for the overlapping area. Please, note that the y-scale does not start at 0%.