Hi,

For the 4 parameters logistic regression model

y = D + ( A - D ) / ( 1 + (x/c )^B)


How to get the 4 cofficients A,B,C,D with a set of given points(x, y) ?

What mathematical method shoud be used?

On the internet, it is easy to find the methods for curve fitting the polynomial equations and 2P logistic regression.