The default rates in the past 15 years for a certain category of loans are 2%, 4%, 7%, 12%, 6%, 5%, 8%, 14%, 10%, 2%, 3%, 2%, 6%, 7%, and 9%. Use the maximum likelihood method to calculate the best fit values of the parameters in Vasicek's model. What is the probability distribution of the default rate? What is the 99.9% worst case default rate?