Dear colleagues: I am using edgeR to examine differential expression
on small RNA data

I noticed this problem also when working with SAGE datasets: when just 
one of the samples
is clearly an outlier, like you can see below for sample 7 (the 
comparison is 1-4 versus 5-8),
there is a call of significant differential expression which seems to be 
inappropriate, or at
least it should be reexamined.

How can we diagnose these situations before checking manually the tag 
counts for all the
significant differential expression calls ? Please note that these are 
tumoral samples, so
an high sample by sample variability is expected in principle..

Thanks a lot in advance,

Alessandro


miRNA_ID 	1.mirna 	2.mirna 	3.mirna 	4.mirna 	5.mirna 	6.mirna 
7.mirna 	8.mirna
hsa-miR-515-3p 	3 	1 	1 	1 	1 	7 	1601 	3
hsa-miR-518e 	4 	0 	1 	0 	1 	2 	1715 	2
hsa-miR-520d-3p 	0 	0 	0 	0 	0 	1 	243 	0
hsa-miR-519c-3p 	0 	0 	0 	0 	0 	1 	248 	0
hsa-miR-520f 	0 	0 	0 	0 	0 	0 	163 	0
hsa-miR-519d 	12 	1 	0 	1 	1 	4 	1754 	1
hsa-miR-520h 	0 	0 	0 	0 	0 	0 	189 	2
hsa-miR-519c-5p 	0 	0 	0 	0 	0 	0 	123 	0
hsa-miR-520g 	16 	1 	1 	4 	2 	4 	1917 	2
hsa-miR-518b 	5 	0 	0 	1 	1 	3 	686 	1
hsa-miR-517a 	100 	5 	4 	2 	6 	45 	10024 	3



miRNA_ID 	logConc 	logFC 	P.Value 	adj.P.Val
hsa-miR-515-3p 	-15.09154 	-8.61753 	0.00000 	0.00082
hsa-miR-518e 	-15.30278 	-9.22926 	0.00000 	0.00110
hsa-miR-520d-3p 	-18.23592 	-9.46747 	0.00001 	0.00201
hsa-miR-519c-3p 	-17.98705 	-9.01722 	0.00002 	0.00338
hsa-miR-520f 	-32.04992 	-35.93228 	0.00002 	0.00338
hsa-miR-519d 	-14.46073 	-7.61177 	0.00003 	0.00338
hsa-miR-520h 	-18.02925 	-8.34496 	0.00003 	0.00338
hsa-miR-519c-5p 	-32.25620 	-35.51970 	0.00004 	0.00382
hsa-miR-520g 	-14.16219 	-7.27220 	0.00005 	0.00382
hsa-miR-518b 	-15.70611 	-7.39997 	0.00006 	0.00382
hsa-miR-517a 	-11.74423 	-7.21374 	0.00006 	0.00382



R version 2.15.0 (2012-03-30)
Platform: x86_64-pc-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] edgeR_2.6.0  limma_3.12.0


-- 

Alessandro Guffanti - Head, Bioinformatics, Genomnia srl
  Via Nerviano, 31 - 20020 Lainate, Milano, Italy
     Ph: +39-0293305.702 Fax: +39-0293305.777
             http://www.genomnia.com
"When you're curious, you find lots of interesting things to do."
(Walt Disney)



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