descriptive statistics:组织和总结信息,为自身(可以是population也可以是sample)审视和探索,
inferential statistics.从sample中推论population情况并评价推论可信度
在population中精挑细选出sample
Observational Studies:观察
and Designed Experiments:施加控制和影响,再观察
Observational studies can reveal only association(即事实一与事实二有关系), whereas designed experiments can help establish causation(事实一导致了事实二)