16.5 ISO 9001

Overview

The benefit/cost ratio (B/CR) of software process improvement (SPI) methods is a ratio of benefits to costs. B/CR is how much money is gained from a SPI method. It is the economic magnitude of a new and improved software process. B/CR is an instant measure of how much additional money we have gained , saved, or received from using a SPI method. In other words, B/CR tells us whether the SPI method was worth all of the time, trouble, expense, and investment. There are only two parts , terms, or components to this very simple equation: benefits and costs. All we have left to do is identify the benefits of our chosen SPI method and the costs of our chosen SPI method. Therein lies the challenge ” to determine which benefits to use, and which costs to use in the B/CR model.

The benefits are the difference between the software maintenance and total life cycle costs. The costs are estimated before and after the introduction of the SPI method. That is, we subtract the new software maintenance and total life cycle costs after introducing the SPI method from the old costs. This assumes that the software maintenance and total life cycle costs of the new SPI method are lower, resulting in cost savings. We have already shown this to be the case for the SPI methods examined here.

The costs, on the other hand, require some selective analysis. What costs constitute the cost term of the B/CR equation? Should we use total costs? Should we use total life cycle costs? Should we use software development and maintenance costs? The answer is not so obvious. The costs that we will use for the B/CR model consist of training, process, product, preparation, assessment, and inspection costs. We will exclude development costs, test costs, and maintenance costs. Why? The costs that we will include consist of all of the special, new, or additional costs that are necessary to introduce the SPI method. Software development, test, and software maintenance costs are the assumed baseline. They must be performed in spite of the new SPI method. They are the platform from which we are departing with the introduction of the new SPI method.