The specific form can be determined from the general form by establishing the values of the parameters of the model through either:

1. estimation - statistical inference procedures are applied to failure data taken for the program, or
2. Prediction - determination from properties of the software product and the development process (this can be done before any execution of the program).

Once the specific form has been established, many different characteristics of the failure process can be determined. For many models there are analytic expressions for:

1. the average number of failures experienced at any point of time,
2. the average number of failures in a time interval,
3. the failure intensity at any point in time,
4. the probability distribution of failure intervals

A good software reliability model has several important characteristics. It

1. gives good predictions of future failure behaviour,
2. computer useful quantities
3. is simple,
4. is widely applicable, and
5. is based on sound assumptions.