Skip to content

Multiple ANOVA tests

4 messages · Imri, Michael Lawrence

Original
Imri
# 
Hi all -
I'm trying to do multiple one-way ANOVA tests of different factors on the
same variable. As a result I have a list with all the ANOVA tables, for
exemple:

$X11_20502
Analysis of Variance Table

Response: MPH
           Df  Sum Sq Mean Sq F value    Pr(>F)    
x           3   369.9   123.3   6.475 0.0002547 ***
Residuals 635 12093.2    19.0                      
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 

$X11_21067
Analysis of Variance Table

Response: MPH
           Df  Sum Sq Mean Sq F value Pr(>F)
x           1    26.7    26.7  1.3662 0.2429
Residuals 637 12436.4    19.5               

$X11_10419
Analysis of Variance Table

Response: MPH
           Df  Sum Sq Mean Sq F value    Pr(>F)    
x           3   527.8   175.9   9.361 4.621e-06 ***
Residuals 635 11935.3    18.8                      
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 

My question is how can I extract from this list, just the Pr(>F) values for
each x ?
Michael Lawrence
# 
#create some data
y=rnorm(20)
x=factor(rep(c('A','B'),each=10))

#run the anova
my_aov = aov(y~x)

#summarize the anova
my_aov_summary = summary(my_aov)

#show the anova summary
print(my_aov_summary)

#lets see what's in the summary object
str(my_aov_summary)

#looks like it's a list with 1 element which
#in turn is a data frame with columns.
#The "Pr(>F)" column looks like what we want
my_aov_summary[[1]]$P

#yup, that's it. Grab the first value
p = my_aov_summary[[1]]$P[1]
On Wed, May 27, 2009 at 7:11 AM, Imri <bisrael at agri.huji.ac.il> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Imri
    

    

      
      #
    

  


  

      
Thanks for the answer!!!
I Know how to extract the Pr(>F) value from single ANOVA table, but I have a
list of many ANOVA tables recived by :
a<-function(x)(aov(MPH~x))
q<-apply(assoc[,18:20],2,a) # just for example, I have more than 3
factors(x)

            

      
      
      
    

        
$X11_20502
             Df  Sum Sq Mean Sq F value    Pr(>F)    
x             3   369.9   123.3   6.475 0.0002547 ***
Residuals   635 12093.2    19.0                      
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 
246 observations deleted due to missingness

$X11_21067
             Df  Sum Sq Mean Sq F value Pr(>F)
x             1    26.7    26.7  1.3662 0.2429
Residuals   637 12436.4    19.5               
246 observations deleted due to missingness

$X11_10419
             Df  Sum Sq Mean Sq F value    Pr(>F)    
x             3   527.8   175.9   9.361 4.621e-06 ***
Residuals   635 11935.3    18.8                      
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 
246 observations deleted due to missingness

            

      
      
      
    

        
Length Class       Mode
X11_20502 1      summary.aov list
X11_21067 1      summary.aov list
X11_10419 1      summary.aov list
 How can I extract all the Pr(>F) values from q (not one by one)?

Thanks
Imri

        
Mike Lawrence wrote:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Michael Lawrence
    

    

      
      #
    

  


  

      
you could use ldply from the plyr package:

p = ldply(q,function(x){x$P})

Without you data I can't confirm that works, but something like that
should do it

        
On Wed, May 27, 2009 at 9:23 AM, Imri <bisrael at agri.huji.ac.il> wrote: