The reasons there are two main expressions for population and sample" is that one is biased estimator 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。

youdao

And the other thing you can do is take self reports like the ones you're doing, hopefully do enough of them, and a random enough sample of the population, that you can extrapolate from that sample to the whole population, and try to estimate what people are eating in that way.

还有其他可以做的,比如大家正在做的这种个体调查,希望能把它做的充分些,如果有充足的随机样本,就可以从样本推断出,整个总体,从而推断哪类人有这样的饮食习惯

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

This is very important,which is why I am doing it: "If we want to know how fast a human being can run, then it is no use to average out the speed of a "good sample" of the population; it is far better to collect Olympic gold medal winners and see how well they can do.

这话非常重要，是我作这个研究的原因：,“如果想知道人类最快能跑多快，那从好的样本中测出平均数是“,没用的;,而应该收集田径类奥运冠军的信息,看他们能跑多快。

哈佛公开课 - 幸福课课程节选

In a poll, why must there be a clear and accurate link between sample and population?

CNN: The Polls

The new results are the first from an ongoing study intended to assess mental health in a representative population sample, balanced for demographics and including people who returned home and those who remain dispersed around the country.

NPR: Mental Issues Surge, Suicide Rates Flat Post-Katrina

These analyses are based on the assumption that the animals collected represent a randomly selected and thus representative sample of the population.

ECONOMIST: Animal personalities