P-Val not significant for diff expressed genes

[chirag.parsania]

Dear All,
I have doubt regarding P-Val of diff expressed genes. kindly help
Doubt : I have list of genes which have p-val not significant (>= 0.05) and all the genes are diff expressed (log 2 FC >= 1 or Log2FC <= -1).
Number of the genes is very huge (~3.5k). looking at the Log2 of all these genes, they are diff expressed then why p-val are not significant ? How the p-val been calculated for diff expressed genes? Which factors are taking in the consideration in p-val calculation for diff exp genes?
Here, if i consider p-val (<= 0.05 )for the diff exp genes then probably I miss the many genes which are truly diff expressed.
These results are generated through DESeq.I have also tried cuffdiff for this data and same results i got from there also
FYI : I don't have any technical replicants for this data
Please give your inputs and possible explanation
Ant help would be appreciated
Thank you

[dpryan]

This has nothing to do with differential expression, rather it's a failure to understand basic statistics. In short, fold-change isn't an effect size. It has no incorporation of variance, by it's vary nature. However, the reliability of a measurement is dependent on both the fold-change and the variance.