Sarah - 1 year ago 55
R Question

# How do I print the variance of an lm in R without computing from the Standard Error by hand?

Simple question really! I am running lots of linear regressions of

`y~x`
and want to obtain the variance for each regression without computing it from hand from the Standard Error output given in the
`summary.lm`
command. Just to save a bit of time :-). Any ideas of the command to do this? Or will I have to write a function to do it myself?

``````m<-lm(Alopecurus.geniculatus~Year)
> summary(m)

Call:
lm(formula = Alopecurus.geniculatus ~ Year)

Residuals:
Min      1Q  Median      3Q     Max
-19.374  -8.667  -2.094   9.601  21.832

Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 700.3921   302.2936   2.317   0.0275 *
Year         -0.2757     0.1530  -1.802   0.0817 .
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 11.45 on 30 degrees of freedom
(15 observations deleted due to missingness)
Multiple R-squared: 0.09762,    Adjusted R-squared: 0.06754
F-statistic: 3.246 on 1 and 30 DF,  p-value: 0.08168
``````

So I get a Standard Error output and I was hoping to get a Variance output without calculating it by hand...

If you want the residual variance, it's: `(summary(m)\$sigma)**2`.
If you want the variance of your slope, it's: `(summary(m)\$coefficients[2,2])**2`, or `vcov(m)[2,2]`.