Question about FC/ ratio

Question

[kanwarjag]

I have to clarify another step from my previous question @ log ratio in gene expression array

If two values are A-32 B -18 If I have to present data as FC and log FC For FC it will be 32-18= 1.7 this will be a linear FC

and log FC= LogA-logB will be 5-4.1=1.19= 0.2 when we use log values of A and B, Do we again shift the results to log value- log 1.19

Or we present logFC as log of linear FC- meaning log (1.7)= 0.8 What is the best and correct way of presentation.

Answer 1

[JC]

The math for those are:

A = 32 -> log(A) = 1.50514997832
B = 18 -> log(B) = 1.2552725051

FC(AB) = A / B = 32 / 18 = 1.77777777778 -> log(FC) = log(1.77777777778) = 0.24987747321

logFC(AB) = log( A / B) = log(A) - log(B) = 1.50514997832 - 1.2552725051 = 0.24987747322

[kanwarjag]

Thanks. So RamsRS has suggested "And if your numbers are starting off in log space (since you have A - B depicting a ratio), then C is already a log value and does not need to transform to log space". @ log ratio in gene expression array I want to clarify this issue; so one has not to transform log C also. that was the confusion.