Another useful ratio is for review time divided by development time .In the PSP, the general guideline is that you should spent producing it. This means that for every hour of coding ,for example, you should spend at least half an hour doing a code review The same ratio for design and design review time, requirements and requirements review time, and forth. One way to determine the reasonableness of these review ration is by comparing defect-injection and remove rates. Table 8.4 shows the defect-injection rates for detailed design and coding for the same 810 developers on the 3240 programs they wrote with PSP2 and PSP
2.1 The developers. injected 9302 defects in 4624 hours of design and injected 19,296 defects in 4160 hour of coding . These rates are 2.01 defects injected per hour in detailed and 4.64 defects injected per hour during coding. The table also shows the defect-removal rates for these same developers in design reviews and code reviews Here ,the average removal rates are 3.32 defects per hour in design review and 6.04 defect per hour in code review. The ratios of these developers must spent at least 76.8% of their coding time in code review to expect to find the defects they inject Similarly. they must spend at least 60.5% of their design time in design reviews to find their design time in design reviews to find their design defects.
The PSP guideline of 50% is sufficiently close to these values to provide a simper and easy-to-remember target. However. you should view it as a minimum with the optimum close to 70% As you gather data on your own performance, select the guideline that best fits your personal data