Hello all, I'm running a probit regression in Minitab to determine the LC50 of particular drugs on mosquitoes. Minitab doesn't have the option to log base 10 transform the concentration, so I created a column and transformed the concentration values using the calculator, adding +1 to the equation so the control values would be at zero (instead of undefined). When I ran the analysis, I got a 1.97, which I assumed I'd subtract 1, and then backtransform. However, this doesn't fit what I was seeing in my data. When I transformed without the +1, I got approximately the same number. Does Minitab autocorrect the +1 on its own? Should I just transform the data without a +1?
Dear Staci Dreyer;
to calculate Lc50/Lt50, you can use SAS software. I hope the following file will help you to analysi your data. it includes very clear synthaxs to run your data.