Graphs depicting qPCR fold change

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loudowns
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Joined: Mon Jun 30, 2014 4:13 pm

Graphs depicting qPCR fold change

I am interested in hearing people opinions about what is the best/accepted way to display the fold change values in a graph, specifically the fold change axis scale?

I have seen it presented in one of 2 ways 99% of the time, but neither of these are ideal as far as I can tell:
1. On a scale from 0 to whatever, where values between 0 and 1 represent down-regulation, and values >1 represent up-regulation. But the problem with this method is that it is harder to appreciate the extent of down-regulation.
2. Using inverse values where negative values (<-1) represent down-regulation and positive values (>+1) represent up-regulation. However, the problem with this approach is that a fold change of +1 is essentially equal to -1, and there shouldn't be anything between these values. So this is wasted space, but more to the point, the difference between, say -1.1 and +1.1, looks much bigger than it actually is.

Why do people not use graphs that show the inverse values, but cut out the section between -1 and +1? So the y-axis may, from the bottom up, go -2, +/-1, 2 etc? Is it purely because the axis would not me mathematically accurate?

I have attached a PDF with the same data plotted in all three ways discussed above.
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