The reasons there are two main expressions for population and sample" is that one is biasedestimator and the other is not."
“母体”与“样本”之所以有两种表达公式，是因为一个是有偏估计，另一个则不是。
2
We give the approximation formulas of the variance of the sample ratio estimator for a population mean and its asymptotically non-biasedestimator in multi-stage sampling.
Instead of using the homomorphic filter which is used to get rid of multiple noise and is a biasedestimator, this algorithm translates speckle into locally stationary additive white noise.