A clear batch-specific bias was detected in the measured expressions of both the UHRR and clinical samples.
A clear batch-specific effect was observed in the raw data when the correlations of identical UHRR samples were assessed over all available pairs across the five runs processed on different days as illustrated in Figure 1.
In fact, clear batch effects could be seen from PCA plot or unsupervised clustering and the first principal component from PCA was significantly associated with the batch effects in both datasets regardless of normalization methods (Table 1).
Additionally, the plot highlighted the existence of 7 clear batches in simply combined datasets (A); however, COMBAT-implementation method greatly improved the appearance of plot (B).
Due to a clear scan date batch issue (Additional file 3, Figure A), we focused our analysis on the data generated in years 2006 and 2007 (hence excluding the two samples scanned in 2005 as well as the 36 samples processed in 2008).
Additionally, a clear positive relation between batch IBS-TAG production rate (rTAG, IBS, batch) and I IBS, batch was observed in our study, for both reactor configurations.
However, this definition should not be taken as absolute, because a clear definition of a batch results from careful examination of the data set, in order to identify what is an appropriate batch variable other than the processing group, as the slide or the array (i.e., position on the slide).
These 2 main clusters are a clear example of inevitable batch effects since the supplier of the hybridization agents changed the chemical components used in the production process in the year 2007 (personal communication; Affymetrix).
Although no differences were observed for the total exposure (AUC) of the different batches, a clear relationship between dissolution and Cmax was observed.
Behind the glass of the Preston & Thomas display lie sausages and crispy bits, a clear space where the fresh batch of fish will soon sit.
