[R] t value two.sided and one.sided
Marc Schwartz
marc_schwartz at comcast.net
Fri May 11 02:11:32 CEST 2007
On Fri, 2007-05-11 at 00:14 +0100, gatemaze at gmail.com wrote:
> Hi,
>
> on a
> > summary(lm(y~x))
> are the computed t-values for two.sided or one.sided. By looking on some
> tables they seem like they are for two.sided.
Yep.
> Is it possible to have them
> for one.sided? If this makes sense...
Yep.
Using the example model 'lm.D9' from ?lm:
summ.lm <- summary(lm.D9)
> summ.lm
Call:
lm(formula = weight ~ group)
Residuals:
Min 1Q Median 3Q Max
-1.0710 -0.4938 0.0685 0.2462 1.3690
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 5.0320 0.2202 22.850 9.55e-15 ***
groupTrt -0.3710 0.3114 -1.191 0.249
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 0.6964 on 18 degrees of freedom
Multiple R-Squared: 0.07308, Adjusted R-squared: 0.02158
F-statistic: 1.419 on 1 and 18 DF, p-value: 0.249
Now get the one sided values:
> pt(coef(summ.lm)[, 3], summ.lm$df[2], lower = FALSE)
(Intercept) groupTrt
4.773564e-15 8.754884e-01
> pt(coef(summ.lm)[, 3], summ.lm$df[2], lower = TRUE)
(Intercept) groupTrt
1.0000000 0.1245116
See ?summary.lm, ?coef and ?pt
HTH,
Marc Schwartz
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