title: Evaluation of the similarity of gene expression data estimated with SAGE and Affymetrix GeneChips.
abstract: BACKGROUND
  Serial Analysis of Gene Expression (SAGE) and microarrays have found a widespread application, but much ambiguity exists regarding the evaluation of these technologies. Cross-platform utilization of gene expression data from the SAGE and microarray technology could reduce the need for duplicate experiments and facilitate a more extensive exchange of data within the research community. This requires a measure for the correspondence of the different gene expression platforms. To date, a number of cross-platform evaluations (including a few studies using SAGE and Affymetrix GeneChips) have been conducted showing a variable, but overall low, concordance. This study evaluates these overall measures and introduces the between-ratio difference as a concordance measure pergene.
  
  
  RESULTS
  In this study, gene expression measurements of Unigene clusters represented by both Affymetrix GeneChips HG-U133A and SAGE were compared using two independent RNA samples. After matching of the data sets the final comparison contains a small data set of 1094 unique Unigene clusters, which is unbiased with respect to expression level. Different overall correlation approaches, like Up/Down classification, contingency tables and correlation coefficients were used to compare both platforms. In addition, we introduce a novel approach to compare two platforms based on the calculation of differences between expression ratios observed in each platform for each individual transcript. This approach results in a concordance measure per gene (with statistical probability value), as opposed to the commonly used overall concordance measures between platforms.
  
  
  CONCLUSIONS
  We can conclude that intra-platform correlations are generally good, but that overall agreement between the two platforms is modest. This might be due to the binomially distributed sampling variation in SAGE tag counts, SAGE annotation errors and the intensity variation between probe sets of a single gene in Affymetrix GeneChips. We cannot identify or advice which platform performs better since both have their (dis)-advantages. Therefore it is strongly recommended to perform follow-up studies of interesting genes using additional techniques. The newly introduced between-ratio difference is a filtering-independent measure for between-platform concordance. Moreover, the between-ratio difference per gene can be used to detect transcripts with similar regulation on both platforms.
authors.affiliation: Department of Neurogenetics, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. f.vanruissen@amc.uva.nl
authors.forename: Fred
authors.initials: F
authors.lastname: van Ruissen
authors.forename: Jan M
authors.initials: JM
authors.lastname: Ruijter
authors.forename: Gerben J
authors.initials: GJ
authors.lastname: Schaaf
authors.forename: Lida
authors.initials: L
authors.lastname: Asgharnegad
authors.forename: Danny A
authors.initials: DA
authors.lastname: Zwijnenburg
authors.forename: Marcel
authors.initials: M
authors.lastname: Kool
authors.forename: Frank
authors.initials: F
authors.lastname: Baas
mesh_terms: D045744:Cell Line, Tumor; D016000:Cluster Analysis; D015342:DNA Probes; D018076:DNA, Complementary; D015870:Gene Expression; D005786:Gene Expression Regulation; D006801:Humans; D046228:Microarray Analysis; D015336:Molecular Probe Techniques; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods*; D012313:RNA / Q000378:metabolism; D018075:RNA, Complementary / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012334:RNA, Neoplasm / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D015342:DNA Probes; D018076:DNA, Complementary; D018075:RNA, Complementary; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D012313:RNA