How can I compare results from two different studies?
To reduce any technical variation in your results Olink recommend that samples are randomized prior to analysis and that the results are intensity normalized.
When analyzing results from 2 or more studies analysed at different time points, and where samples can not be considered randomized between the studies, Olink recommend including between 8-16 bridging samples in each study. If possible, these reference samples should be representative for the entire study, for example include all study groups, and should be matrix-matched with other samples.
Using these bridging samples, reference sample normalization can be applied when merging previously normalized data sets.
Reference sample normalization is performed in the following way:
Choose a reference project to normalize towards
For each assay and project, calculate the pairwise difference for each of the overlapping samples with the reference plate
Estimate the project- and assay-specific normalization factor by calculating the median for the pairwise differences calculated in step 2
For each assay and project, add the plate- and assay-specific normalization factor from step 3 to each value, to normalize it to the reference plate chosen in step 1
NPX across plates for each protein including reference samples
NPX across plates for each protein after reference sample normalization