Hierarchical clustering of RMA normalized R7 data.

<p>Each color represents a batch of arrays, which were hybridized and processed at the same time. Batch effects are evident even after normalization and before batch adjustment (A) as arrays are mostly clustered in batches. However, following Empirical Bayes adjustment arrays are clustered based on aged and young phenotypes irrespective of batches (B). Leaf labels: A, aged; Y, young; I, impaired; U, unimpaired; c, control.