Recent research indicates that the effectiveness of antidepressant medication is directly related to the severity of the depression (Khan, Brodhead, Kolts & Brown, 2005).  Based on pretreatment depression scores, patients were divided into four groups based on their level of depression.  After receiving the antidepressant medication, depression scores were measured again and the amount of improvement was recorded for each patient. The following data are similar to the results of the study. Low Moderate High Moderate Moderately Severe   Severe 0.3 1.2 2.2 1.8 3.8 1.7 1.4 2.8 3.2 0.4 0.6 2.6 2.3 1.2 1.6 2.6 2 3.2 1.6 2.2 0.6 1.2 1.6 1 2.7 1 2.2 0.6 1.4 1.6 3.3 2.7 2.2 2.9 3.7 2.6 0.9 0.7 3.4 3.1 2.6 1.7 0.8 1.8 2 1.4 1.6 4.1 1.7 0.9 3.3 2.3 1.6 1.1 3.5 1.4 3.5 1.9 0.4 4.2 1.5 2.3 2.2 2.9 1.4 2.2 2.7 2.8 2.1 1.9 1.9 3.9 1.5 2.7 0.8 1.5 1 3 2.1 3.7 1.5 0.9 2.4 1.9 2.7 3.2 0.8 2.7 2.2 2.9 1.8 1.2 2.4 1.7 3.2 1.3 2.2 2.4 1.1 1 2.6 2 2.4 3.8 0.9 1.3 1.8 1.9 1.7 1.7 1.2 3.8 1.3 0 3.3 3 1.9 2.5 1.1 1.8 0 3.6 1.8 2.9 2.1 3.2 2.9 2.8 3.2 1.8 0.8 2.3 1 3 4.4 2.2 1.8 0.2 2.3 2.3 1.8 4.1 3.6 2.2 1.5 2 2.2 1.9 3.1 2.6 2.7 2.8 2.1 1.3 1.1 2.5 0.7 1.5 0.8 4 0.7 2.6 2.1 3 1.9 1.3 1.7 3.3 3.2 0.9 1.4 2.4 4 0 4 2.2 1.8 1.6 2.8 3.2 2.8 2 0.6 1.3 1.9 2.4 0.6 2.3 1 2.4 1.8 2.4 3.1 0.9 1.8 3.9 This is the summary table for the ANOVA test:   S.S. d.f. M.S. Between 12.783010204082 3 4.2610034013606 Within 168.27714285714 192 0.87644345238095 TOTAL 181.06015306122 195 From this table, you obtain the necessary statistics for the ANOVA: F-ratio:  4.8616980248812 p-value:  0.00278 η2= 0.070600902451238 What is your final conclusion?  Use a significance level of α=0.02. These data do not provide evidence of a difference between the treatments There is a significant difference between treatments   Explain what this tells us about the equality of means.

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Recent research indicates that the effectiveness of antidepressant medication is directly related to the severity of the depression (Khan, Brodhead, Kolts & Brown, 2005).  Based on pretreatment depression scores, patients were divided into four groups based on their level of depression.  After receiving the antidepressant medication, depression scores were measured again and the amount of improvement was recorded for each patient. The following data are similar to the results of the study.

Low
Moderate
High
Moderate
Moderately
Severe
 
Severe
0.3 1.2 2.2 1.8
3.8 1.7 1.4 2.8
3.2 0.4 0.6 2.6
2.3 1.2 1.6 2.6
2 3.2 1.6 2.2
0.6 1.2 1.6 1
2.7 1 2.2 0.6
1.4 1.6 3.3 2.7
2.2 2.9 3.7 2.6
0.9 0.7 3.4 3.1
2.6 1.7 0.8 1.8
2 1.4 1.6 4.1
1.7 0.9 3.3 2.3
1.6 1.1 3.5 1.4
3.5 1.9 0.4 4.2
1.5 2.3 2.2 2.9
1.4 2.2 2.7 2.8
2.1 1.9 1.9 3.9
1.5 2.7 0.8 1.5
1 3 2.1 3.7
1.5 0.9 2.4 1.9
2.7 3.2 0.8 2.7
2.2 2.9 1.8 1.2
2.4 1.7 3.2 1.3
2.2 2.4 1.1 1
2.6 2 2.4 3.8
0.9 1.3 1.8 1.9
1.7 1.7 1.2 3.8
1.3 0 3.3 3
1.9 2.5 1.1 1.8
0 3.6 1.8 2.9
2.1 3.2 2.9 2.8
3.2 1.8 0.8 2.3
1 3 4.4 2.2
1.8 0.2 2.3 2.3
1.8 4.1 3.6 2.2
1.5 2 2.2 1.9
3.1 2.6 2.7 2.8
2.1 1.3 1.1 2.5
0.7 1.5 0.8 4
0.7 2.6 2.1 3
1.9 1.3 1.7 3.3
3.2 0.9 1.4 2.4
4 0 4 2.2
1.8 1.6 2.8 3.2
2.8 2 0.6 1.3
1.9 2.4 0.6 2.3
1 2.4 1.8 2.4
3.1 0.9 1.8 3.9

This is the summary table for the ANOVA test:

  S.S. d.f. M.S.
Between 12.783010204082 3 4.2610034013606
Within 168.27714285714 192 0.87644345238095
TOTAL 181.06015306122 195

From this table, you obtain the necessary statistics for the ANOVA:
F-ratio:  4.8616980248812
p-value:  0.00278
η2= 0.070600902451238

What is your final conclusion?  Use a significance level of α=0.02.

  • These data do not provide evidence of a difference between the treatments
  • There is a significant difference between treatments

 

Explain what this tells us about the equality of means.

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