大数原则是一切社会保险事业普遍遵循的法则。没有一定的参保率（覆盖率），基金统筹量不足，就不可能形成较强的抗风险能力。作为农村医疗保障制度形式之一的合作医疗也概莫能外。因此，多少年来，我们一直把保持和扩大覆盖率作为巩固和发展合作医疗的关键，不敢懈怠。然而在 The principle of large numbers is the general rule followed by all social insurance undertakings. Without a certain coverage rate (coverage rate) and inadequate fund pooling, it is impossible to form a strong anti-risk capability. The cooperative medical system that is one of the forms of the rural medical security system is also beyond exception. Therefore, for many years, we have been maintaining and expanding coverage as the key to consolidating and developing cooperative medical care, and we have not dared to slack off. However, in