总体分布、样本分布、抽样分布的区别
参考自：THREE DISTRIBUTIONS
1.总体分布
The population is the whole set of values, or individuals, you are interested in.
The population which consists of a set of scores (5, 6, 7, 8) which distribute around a parameter mean of 7.00.
2.样本分布（Sample distribution）
The sample is a subset of the population, and is the set of values you actually use in your estimation.
From this population, we can draw a number of samples. Each sample consists of three scores which constitute a subset of the population.
3.抽样分布（Sampling distribution）（样本统计量的分布，每个样本统计量都有一个分布）
样本k阶中心矩、样本k阶原点矩、样本标准差、样本均值、样本方差
Researchers often use a sample to draw inferences about the population that sample is from.
The sample scores distribute around some statistic mean for each sample.
