The author was probably talking about the logistic function being parameterized by 3 parameters, x0, L, and k [1]. The point the author is probably making is th

The author was probably talking about the logistic function being parameterized by 3 parameters, x0, L, and k [1]. The point the author is probably making is that if you are fitting a perfect logistic model to data, 3 data points should be sufficient to determine 3 parameters that unambiguously parameterize the curve. A separate set of 3 parameters also parameterizes the SIR compartmental model (https://en.wikipedia.org/wiki/Compartmental_models_in_epidemiology#The_SIR_model https://en.wikipedia.org/wiki/Compartmental_models_in_epidem...), the solution of which also looks like a logistic curve. But this is a model-based (dynamics-based) solution whereas one may be interested in just fitting the logistic model based on the assumption that it's going to be logistic. [1] https://en.wikipedia.org/wiki/Logistic_function https://en.wikipedia.org/wiki/Logistic_function