Figure 63 shows the portion of the APD model that addresses staffing and experience gain. The construct is very similar to that presented in section 4.3, describing developer experience mix and its relationship to Brooks’ Law.

Figure 64 shows our staffing profile when executing this model. Here the project starts with at a pre-determined mix of New Staff and Experienced Staff (10 and 0). As time elapses, employees gain experience and become Experienced Staff. Note that we never reach a level of 100% of experienced employees, because our staff is changing at the rate of 5% after every sprint (Staff Churn Rate) to model the fact that in real organizations, developers are reassigned to different tasks and efforts regularly.

Over time, as employees gain experience, FCC and Productivity improve. Figure 65 shows how the effect of staff Experience on Productivity increases over time. The effect of experience on FCC shows a similar behaviour.