Logistic Regression Analyses in Dose Response Studies

In dosage response studies the two most commonly used techniques are i) Probit analysis, ii) Logit analysis. Logit analysis is easy to carry out and most practical situations are closer to logit than probit analysis. In logit analysis the function to fit is (t)= ea + at / 1 + ea+at where it is the log dose and (t) is the proportion killed. The parameters and in the function can be estimated by using following methods: Least squares, Method of moments, Weighted least squares, Maximum likelihood both the point and interval estimates for these methods are discussed by taking three practical examples. LD50 is estimated and the intervals constructed. It has been shown that method of weighted least squares gives quite good results.