Figure 4: Concordance log-log scatter plots for Nickel Exposure Study. The plots are part of inter-slide quality control which uses slides developed on different dates and on different PGA print batches with benchmark sera obtained from a pool of four healthy subjects. In this study there were 8 such slides whose development was interleaved with that of study subjects, resulting in 28 combination pairs. The scatter plots show logarithms of raw intensity signals. Numbers above plots are Lin’s concordance correlation coefficient (CCC, left) and Pearson correlation coefficient (right). The latter coefficient ignores linear bias in scale and location, while the former shows the true differences. The figure presents only 4 combinations out of 28, with patterns typical for this study; correlation coefficients for all 28 combinations are shown in Figure 5.