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# Pfaffl calculation for qpcr: what to enter for E value?

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### #1 hianghao

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Posted 20 June 2011 - 05:22 PM

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?

Edited by hianghao, 20 June 2011 - 05:33 PM.

### #2 Trof

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Posted 21 June 2011 - 02:57 AM

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

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### #3 hianghao

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Posted 21 June 2011 - 04:29 PM

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

I thought so. I saw the latter one here:
http://www.protocol-...osts/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...altime-home.htm

Edited by hianghao, 21 June 2011 - 04:34 PM.