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ANOVA: Degrees of Freedom & Critical value

See attached file for clarity.

Can you explain what are the degrees of freedom on this example . (Is it 87 or 89?) and how do I get critical value?

One factor ANOVA

Mean n Std. Dev
5.9 30 1.90 Text message
6.4 30 1.45 Internet
5.2 30 1.58 E-mail
5.8 90 1.71 Total

ANOVA table
Source SS df MS F p-value
Treatment 23.09 2 11.544 4.22 .0178
Error 238.07 87 2.736
Total 261.16 89

Post hoc analysis
p-values for pairwise t-tests
E-mail Text message Internet
5.2 5.9 6.4
E-mail 5.2
Text message 5.9 .0895
Internet 6.4 .0049 .2449

Tukey simultaneous comparison t-values (d.f. = 87)
E-mail Text message Internet
5.2 5.9 6.4
E-mail 5.2
Text message 5.9 1.72
Internet 6.4 2.89 1.17

Critical values for experimentwise error rate:
0.05 2.39
0.01 3.00

Solution Summary

The solution provides step by step method for the calculation of degrees of freedom and critical value of One factor ANOVA. Formula for the calculation and Interpretations of the results are also included.

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