高級化學(an chem)

coefficient of variation, 即係CV = 100% * (s/x)

sigma係population standard deviation, 即係當你個data係用哂個pool入面所有participant既時候, 就用sigma舨代表個precision. 比如全人口普查時得出既收入分佈就可以用佢計.

sample standard deviation (s)就係當你係抽樣做test計平均值, 同真實極有可能有出入時, 就要用s黎計. 例如電話抽問調查收入分佈時就要用呢個.

我地設計一個實驗就係aim at s tends to sigma. 而個s既入面既denominator (N-1), 就係你個degree of freedom. simga既degree of freedom就係無限, 即係無限個sample咁解. 但我地冇可能無限個sample, 所以用confidence level黎代表一個s近唔近sigma.

例如confidence level係90%, 即係你有90% sure個population mean係lie in 負1 sigma至正1sigma入面. 而個confidence interval就係: 括號呢舊就係confidence interval既symbol
(正負z * sigma) = 正負1sigma