更想由其中的特性來得知母體的資訊, 在這之下, 樣本的分配情況就值得加以研究.
- A numerical of a population is called a parameter.
- A sample-based quantity is called a statistic.
A statistic is a numerical valued function of the sample observations.
For example, the sample mean
statistic because its numerical value can be computed once the sample data,
consisting of the values of
X1,...Xn, are available. Likewise, the sample
median and the sample standard deviation are also sample-based quantities so
each is a statistic.
A sample-based quantity (statistic) must serve as our source of information
about the value of a parameter. Three points are crucial:
- Because a sample is only a part of the population, the numerical value
of a statistic cannot be expected to give us the exact value of the parameter.
- The observed value of a statistic depends on the particular sample that
happens to be selected.
- There will be some variability in the values of a statistic over different
occasions of sampling.