[R] Call the Standard Error and t-test probability in linear regression

[(Ted Harding)]

On 02-Mar-2012 IOANNA wrote:
> Hello, 
> I run a linear regression I get the summary, e.g.:
> 
>>  
>    Call: 
>    lm(formula = signal ~ conc) 
>    Residuals: 
>       1        2     3      4      5  
>      0.4  -1.0   1.6  -1.8    0.8  
>    Coefficients: 
>                   Estimate Std.  Error    t value    Pr(>|t|)     
>      (Intercept)  3.60000    1.23288    2.92     0.0615 .   
>      conc          1.94000     0.05033   38.54  3.84e-05 *** 
>    --- 
>    Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1  
>    Residual standard error: 1.592 on 3 degrees of freedom 
>    Multiple R-Squared: 0.998,      Adjusted R-squared: 0.9973  
>    F-statistic:  1486 on 1 and 3 DF,  p-value: 3.842e-0
> 
> I would like to call the probability of the t-test only in order
> to use it separately. For example I 'd like to get: 
> Pr<-3.84e-05 
> 
> Similarly I want to call the standard error of the parameters
> and the function:
> SEconc<-0.05033
> 
> I don't know how to do this. Any help?
> 
> Regards, 
> Ioanna

Hi Ioanna,
If you look at '?summary.lm' and read the section "Value",
you will see that the returned value is a list with several
components, one of which is:

  coefficients: a p x 4 matrix with columns for the
    estimated coefficient, its standard error,
    t-statistic and corresponding (two-sided) p-value.
    Aliased coefficients are omitted.

This is effectively as displayed by summary(lm...)).
So your 

  Coefficients: 
>               Estimate  Std. Error  t value  Pr(>|t|)     
>   (Intercept)  3.60000     1.23288     2.92    0.0615 .   
>          conc  1.94000     0.05033    38.54  3.84e-05 *** 

(apart from the significance codes "." and "***") are the
elements in this p=2 x 4 matrix.

Hence

  summary(lm.r)$coef

would give the full 4x4 matrix (you can abbreviate "coefficients"
to "coef"), and so

  summary(lm.r)$coef[2,4]

will give you the P-value for "conc", and

  summary(lm.r)$coef[2,2]

will give the SE of the estimate of "conc". And so on.

Ted.

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 02-Mar-2012  Time: 13:09:03
This message was sent by XFMail