In part one of our team size series, we looked at Best and Worst in Class software projects and found that using small teams is a best practice for top performing projects. Part two looked at differences in cost and quality between small and large team projects and found that small teams use dramatically less effort and create fewer defects. But simply knowing that small teams perform better doesn’t tell us how small a team to use. Most software metrics scale with project size, and team size is no exception. Management priorities must also be taken into account. Small projects can realize some schedule compression by using slightly larger teams but for larger projects, using too many people drives up cost but does little to reduce time to market:
Larger teams create more defects, which in turn beget additional rework… These unplanned find/fix/retest cycles take additional time, drive up cost, and cancel out any schedule compression achieved by larger teams earlier in the lifecycle.
In a study conducted in the spring of 2011, QSM Consultant Don Beckett designed a study that takes both system size and management priorities into account. He divided 1920 IT projects into four size quartiles. Using median effort productivity (SLOC/PM) and schedule productivity (SLOC/Month) values for each size bin, he then isolated top performing projects for schedule, effort, and balanced performance (better than average for effort and schedule):
In each size quartile he studied, smaller teams achieved better effort and schedule performance, but the optimal team size varied according to whether they excelled at effort performance, schedule performance, or balanced effort and schedule performance. Here are the results for projects in the smallest size quartile:
- Teams of 3 or fewer people were the most likely to achieve balanced schedule and cost/effort performance.
- Teams of 2 or fewer achieved the best cost/effort performance.
- Teams of 2 to 4 delivered the best schedule performance.
- Teams of more than 4 people resulted in dramatically worse cost/effort and schedule performance.
Don summarized the results for all four size bins in the table below. The optimal team size for cost/effort performance increases steadily with project size (green column). For schedule performance (blue column), the relationship is less clear cut. Again, this mirrors the results in part two of our team size series. Projects that want to balance cost and schedule performance should use teams somewhere in between the suggested ranges for best schedule and effort performance.