Calculate variance by hand, result not match

[shizidushu]

> x <- c(-8.5, 1.2, 1.5, 5.6, 2.4, 6.54, 25.21)
> sum((x - mean(x))^2)  / length(x)
[1] 89.53117
> var(x)
[1] 104.453

Why the result is not match?

[Yarnabrina]

R uses the sample version of variance, i.e. the one with denominator n - 1 instead of n. It's preferable as it gives unbiased estimate to population variance. See below:

x <- c(-8.5, 1.2, 1.5, 5.6, 2.4, 6.54, 25.21)

sum((x - mean(x)) ^ 2) / length(x)
#> [1] 89.53117

sum((x - mean(x)) ^ 2) / (length(x) - 1)
#> [1] 104.453

var(x)
#> [1] 104.453

^{Created on 2019-07-05 by the reprex package (v0.3.0)}

Hope this helps.