**0**wrote:

Hi all, I have RNAseq data from 3 biological replicates but only have log2 values for gene expression quantification.

I was wondering if there are any "cons" against using log2 values for calculating the standard deviation? Converting all expression values to absolute values using the In2 function is easy enough but when I calculate the SD using log2 vs base values, I always end up with different values. Surely this cant be right? Does anyone have a preference for using base means values over log2 values for this type of analysis?

Many thanks in advance,

Ricky

PS: When comparing log2 and base mean values I do convert them into Ln2 and/or log2 to compare them both on the same scale, ie I am not comparing SD of Ln2 with log2 values.

**4.7k**• written 20 months ago by rjobmc •

**0**

I'm not clearly understanding what are you doing. But, sd will surely be different if you "scale" the data differently. By taking log, you are essentially scaling the data on a logarithmic scale.

Standard deviation is a measurement of

spread of dataaround the mean of the data. When you take log, it shrinks the data, as well as its spread and consequently the standard deviation.4.7k