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