Empirical array quality weights in the analysis of microarray data.
BACKGROUND
Assessment of array quality is an essential step in the analysis of data from microarray experiments. Once detected, less reliable arrays are typically excluded or "filtered" from further analysis to avoid misleading results.


RESULTS
In this article, a graduated approach to array quality is considered based on empirical reproducibility of the gene expression measures from replicate arrays. Weights are assigned to each microarray by fitting a heteroscedastic linear model with shared array variance terms. A novel gene-by-gene update algorithm is used to efficiently estimate the array variances. The inverse variances are used as weights in the linear model analysis to identify differentially expressed genes. The method successfully assigns lower weights to less reproducible arrays from different experiments. Down-weighting the observations from suspect arrays increases the power to detect differential expression. In smaller experiments, this approach outperforms the usual method of filtering the data. The method is available in the limma software package which is implemented in the R software environment.


CONCLUSIONS
This method complements existing normalisation and spot quality procedures, and allows poorer quality arrays, which would otherwise be discarded, to be included in an analysis. It is applicable to microarray data from experiments with some level of replication.
Ritchie
Matthew E
ME
Bioinformatics Division, The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia. mritchie@wehi.edu.au
Diyagama
Dileepa
D
Neilson
Jody
J
van Laar
Ryan
R
Dobrovic
Alexander
A
Holloway
Andrew
A
Smyth
Gordon K
GK
D000465:Algorithms; D000704:Analysis of Variance; D003627:Data Interpretation, Statistical; D020869:Gene Expression Profiling / Q000379:methods; D016014:Linear Models; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D012984:Software