# Pfaffl calculation for qpcr: what to enter for E value? - (Jun/20/2011 )

In the calculation of relative quantification (Pfaffl 2001), the E value is replaced by E in what form? Lets say E=105%, in the formula we put E as 1.05 or 2.1? I think it should be 2.1 because if E is 100%, it'll be 1, and 1^x is always 1.

However i read an older post suggesting that it should be E=1 + amplification efficiency%; ie.: 105% > 1+1.05 = 2.05.

Can anyone verify which is the correct one? If the latter is correct, why is it so?

-hianghao-

The last suggestion seems illogical to me. I would use 2.1.

-Trof-

Trof on Tue Jun 21 10:57:08 2011 said:

The last suggestion seems illogical to me. I would use 2.1.

I thought so. I saw the latter one here:

http://www.protocol-online.org/biology-forums-2/posts/12249.html

But today i found this

"There is some ambiguity in how people define efficiency. Some people say that if you copy 90% of your DNA in a cycle, so that you end up with 1.9 times as much, the efficiency is 1.9, and this is the definition that the Pfaffl equation uses."

http://pathmicro.med.sc.edu/pcr/realtime-home.htm

-hianghao-