4
計算方差並且基於Wikipedia描述標準偏差計算方差ANS標準偏差給出不同的結果變種()和SD()在R.不同的結果作爲R
方差:4與4.571429。標準差:2與2.13809。
任何建議或解釋?
> df <- c(2,4,4,4,5,5,7,9)
> df.length <- length(df)
> df.length
[1] 8
> df.mean <- sum(df)/df.length
> df.mean
[1] 5
> df.difference <- (df - df.mean)**2
> df.difference
[1] 9 1 1 1 0 0 4 16
> sum(df.difference)
[1] 32
> df.variance <- sum(df.difference)/df.length
> df.variance
[1] 4
> df.standard.deviation <- sqrt(df.variance)
> df.standard.deviation
[1] 2
> # mean, var and sd (default R)
> mean(df)
[1] 5
> var(df)
[1] 4.571429
> sd(df)
[1] 2.13809
Thnx!我發現了一些關於此主題的其他信息:[PDF](http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&ved=0CG4QFjAG&url=http%3A%2F%2Fdigitalcommons .unl.edu%2Fcgi%2Fviewcontent.cgi%3Farticle%3D1008%26context%3Dimseteach&ei = Qnq1UrvRM-KQ0AWdl4DQDQ&usg = AFQjCNErI6wFPfD2oz9xVu_1E6EQ37sGpA&sig2 = zyts5YqTDGbXjEFC9LDKvA&bvm = bv.58187178,d.d2k)and [Youtube](http://www.youtube.com/看?v = 92s7IVS6A34)。 – Rene