当团队工作需要进行大量的信息交流和协调时，这一点尤为重要。对于大多数任务而言，4或5人是最优人数，一旦超过10或12人，团队表现和人际关系确实会受到影响。许多经过精心设计的研究表明，发生这种状况的原因在于认知超载。比起3、4个人的团队，协调10位队友的活动、同时还要跟踪他们古怪的行为和情绪变化，这个难度要大得多。为什么海豹突击队(Navy Seals)使用4人战斗小组，麦肯锡公司(McKinsey)的项目小组通常由4名咨询师组成？这就是原因所在。二战期间，美国海军陆战队最初采用12人战斗分队，但很快就恢复为4人小组。这是因为，士兵们突然变得萎靡不振，战斗力随之大幅下降。一项由哈佛大学商学院( Harvard University Business School)教授梅丽莎•瓦伦丁和艾米•埃德蒙森主持的研究发现，当一家大型医院的急诊科把医生和护士分为4个不同的6人诊断团队（而不是尝试着作为一个大组进行运营）之后，医护人员的沟通质量和信任程度大幅改善，就连病人等待就诊的平均时间也从8个小时骤降至5个小时。
My Stanford University colleague, Huggy Rao, spent seven years studying how organizations scale up excellence. We discovered that the process happens largely through teams -- by growing new teams at the right rate in the right way and weaving together the efforts of multiple teams across the company.
Such dynamics are crucial to even tiny young companies. For example, Pulse News, maker of a "news aggregator" app, was started in 2010. Performance problems began to flare up after the company grew to just eight people. So founders Akshay Kothari and Ankit Gupta split Pulse into three small teams. Almost immediately, the young company started producing better software and doing it faster -- and people were getting along better and helping each other solve problems.
When the company expanded to 12 people (working in four teams, all in the same room), each team maintained a bulletin board that communicated their current work to everyone at Pulse. Every afternoon, each team gave a short talk to the company about what they were working on and where they needed advice and help. Pulse continued to rely on small teams as it grew to 25 employees and 30 million users; the company was bought by LinkedIn (LNKD) for $90 million in 2013.
Whether you are growing a startup like Pulse, opening multiple new locations, or spreading new practices across an existing organization, we identified five hallmarks of effective teams that will help you sustain excellence as you grow an organization or expand a program's reach.
Keep teams small
This is especially important when teams do work that requires intensive information exchange and coordination. For most tasks, four or five is optimal, and once teams get larger than 10 or 12, performance and interpersonal relationships really suffer. Many careful studies show that this happens because of cognitive overload. It is far more difficult to coordinate your activities and to keep track of the quirks and moods of 10 teammates than three or four. That is why, for example, the Navy Seals use four-person combat teams and McKinsey engagement teams usually have four consultants. In World War II, the U.S. Marines used 12-person combat teams at first, but quickly reverted to four-person teams because so many performance and morale problems reared their ugly heads. And a Harvard University Business School study by Melissa Valentine and Amy Edmondson found that when the emergency department of a large hospital assigned doctors and nurses to four different six-person pods (rather than trying to function as one big group), not only did communication and trust improve dramatically, waiting time for the average patient dropped from eight hours to five hours.
Use hierarchy to defeat bad bureaucracy
As organizations grow, in addition to dividing large teams, you will need to add a few more layers and a bit more process to weave together what happens across teams. Look at Pulse. After they divided into four teams (each with a leader) they used the bulletin boards and brief afternoon reports to foster communication and coordination across the four teams. Hierarchy, process, and manager are sometimes treated as dirty words. Yet as organizations get larger and more complex, these are necessary measures so long as they are used in small doses and with proper precautions. Chris Fry, who leads engineering at Twitter (TWTR), emphasizes that when rules, roles, and processes cause people "to feel as if they are walking in muck," wise leaders use the hierarchy to repair the bureaucracy.