[BioC] Determining Synergy in MA expts

[Kasper Daniel Hansen]

As another poster have said: you are looking at interactions.  
Basically you have a scale problem here: you have a synergistic  
effect on one scale but not on the other. Because log converts  
multiplication to addition, a synergistic effect on a log scale is  
different than a synergistic effect on the original scale.

 From a naive point of view, this is bewildering. You need to be  
precise wrt. what you mean by a synergistic effect and then realize  
that this definition is not scale independent (however strange that  
may seem).

Kasper

On Nov 8, 2005, at 8:55 AM, Lance Palmer wrote:

> I am interested to know how one may determine if two conditions can  
> have
> synergistic effects.  For example, lets say we expose cells to two
> conditions, X and Y.  We have four microarray chips.
>
>
>
>             0          X          Y          X+Y
>
>
>
> Lets suppose the following raw data
>
>
>
>             8          2046     16        4096
>
>
>
> Log2 of those numbers
>
>
>
>             3          11        4          12
>
>
>
> Log fold change vs no stimuli
>
>
>
>                         8          1          9
>
>
>
> Fold change
>
>
>
>                         256       2          512
>
>
>
> Raw change
>
>
>
>                         2038     8          4088
>
>
>
>
>
>
>
> If you look at the fold change one can say there is no synergistic  
> effect
> since the log fold change of 9 can be explained by the 2**8  
> increase and the
> 2**1 increase.  (or I could say the 512 comes from the 256x  
> component and 2x
> component)
>
>
>
> If you look at the raw change, it appears to be synergistic since
> 2038+8<<<4088.
>
>
>
> I am not a mathematician so I don't know which would be the proper  
> way to
> look at this.  Would an example like this be synergistic.  And what  
> is the
> best way to approach this.
>
>
>
>
>
>
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>
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