Buhlmann-Strauss

Hi

I'm using the BS credibility model to come up with a weighted premium for commercial motor. I have a couple of questions which I was hoping for some feedback on.

In coming up with Tao and Sigma, is there a minimum size in terms of vehicle exposure years, claims etc. that you should use. My fleet size consists of about 500 commercial fleets.
In the formula z = w/(w+k), is there a minimum w below which z is 0. Currently, I don't have a minimum in my formula.

Regards


Buhlmann-Strauss