[R-sig-eco] EC50 Calculations using Insect Size

[Katie Harding]

I have insect size measurements that I fit to a Weibull curve to determine EC50.  This is my model fit:model=nls(y~SSweibull(x,asym,drop,lrc,pwr))
I need to use the untreated buffer samples as the maximum size (the left most asymptope).  If I put the doses as 0,1,2,4,8,16,32,64,128 ppm, I get error messages indicating that 0 values for x are inappropriate.  This is the error message:Error in qr.default(.swts * attr(rhs, "gradient")) :   NA/NaN/Inf in foreign function call (arg 1) 
I found that I get more consistent results when I put 0.01 for the dose of the untreated controls.  I was wondering if there was a convention to follow when using untreated buffer samples in EC50 calculations.  Cheers,Katie

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