Fig. 1

Principal component analysis of the 211 HG-U133A arrays, before (a) and after (b) removal of study effects and corresponding plots for the 150 HG-U133 + 2 arrays (c and d). Different studies (identified by database accession numbers) are represented with different colors, and increasing age of the individual from whom the biopsy was taken is indicated by the increasing dot size. The relatively strong study effect seen even after normalization is removed after the adjustment