Modified Variance Estimation for Unequal Probability Sampling without Replacement When the Size of Sample Is Larger than Two

In order to solve the problem of computing complex variance estimator for unequal probability sampling without replacement, this paper uses Hajek approach and obtains the approximation of joint inclusion probability. Thus, the Hajek variance approximation and the estimator of Hajek variance are acquired. At last, we conclude that unequal probability sampling without replacement is easily implemented when the size of sample is larger than two because of the simplicity of computing variance through the analysis of practical data.