Representing qRTPCR data

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Mol-Bio-Guy
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Representing qRTPCR data

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Hi all,
    So I've come across a bit of a conundrum. My PI wants me to represent the delta-CT on a linear scale (says she thinks linear, not log), and so wants me to "simply" convert the delta-CT to "2-to-the-negative-power" of the delta-CT. Sounds easy, but I've hit a wall in terms of how to proceed.

    The problem arises from the fact that I have multiple biological replicates in two groups, and she wants the mean of each group and it's standard deviation (SD) represented as fold-change of the control RNA.

    Here's the catch: Do I convert to the linear value before I calculate the mean and SD, or do I calculate the mean and SD of the delta-CT values and then convert those to the fold-change?

    I thought that this would be equivalent, but the two methods give you quite different results (SEE ATTACHED). So which one is the right way to represent this? OR, as may be the case, is the very prospect of representing the delta-CT value this way flawed (if so, please try to explain it to me in a way a non-statistician could comprehend)? All and any advice would be greatly appreciated.

Thanks,
Guy

Sami Tuomivaara
Sami Tuomivaara's picture
Mol-Bio-Guy,

Mol-Bio-Guy,

I think you should get the same answer either way. And, if you look at the averages, they are the same (I suppose the small difference between the red treatments is due to rounding error), as expected, irrespective of the order of linearization/calculation. Maybe you didn't do the exatly same mathematical treatment for the +/- SD values... they should behave identically to the average value...

Cheers,