[R] Anova

[Jose Iparraguirre]

Hi, 

You can use the car package and choose Type-III test.
Also, have a look at the package easyanova.
Regards,
José

José Iparraguirre
Chief Economist
Age UK


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of humming-bird
Sent: 27 November 2012 10:12
To: r-help at r-project.org
Subject: [R] Anova

Hi everyone,

I am new to this forum and also new to statistics and I would appreciated it
if someone would take some time to answer my question.

I am analyzing companies in regard to their leverage. I categorized the
companies into 3 groups: small, mid and large. For the group small, I have
55 debt multiples, for mid 42 and for large 72. (Unfortunately I can not
provide my data because it is confidential.)
I am now trying to find out whether the mean debt multiples are
significantly different for the 3 different groups. For this reason I
calculated an anova table with the aov function and to display the results
for each "pair" I did the tukey.hsd function.
Now my question: Am I allowed to use these functions given that my data is
unbalanced? Can use I read several times that aov is only valid for balanced
data? If not, is there another function that I can use?

Thank you very much for your answers.


Call:
aov(formula = Debt.Ebitdax ~ Company.Size, data = Anetdebtx2003)

Terms:
Company.Size Residuals
Sum of Squares 302.3089 926.2174
Deg. of Freedom 2 166

Residual standard error: 2.362123 
Estimated effects may be unbalanced

> summary(Anovanetdebtx2003)
Df Sum Sq Mean Sq F value Pr(>F) 
Company.Size 2 302.3 151.15 27.09 6.58e-11 ***
Residuals 166 926.2 5.58 
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 


> TukeyHSD(Anovanetdebtx2003)
Tukey multiple comparisons of means
95% family-wise confidence level

Fit: aov(formula = Debt.Ebitdax ~ Company.Size, data = Anetdebtx2003)

$Company.Size
diff lwr upr p adj
Mid Market Buyout-Large Buyout -1.446292 -2.530922 -0.3616617 0.0054123
Small Buyout-Large Buyout -3.112143 -4.112545 -2.1117420 0.0000000
Small Buyout-Mid Market Buyout -1.665852 -2.810574 -0.5211300 0.0021037



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