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# Statistics: Tests of Between-Subject Effects

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Question 12

Choose the statement that best applies to the following example and SPSS output.
Dana wishes to assess whether vitamin C is effective in the treatment of colds. To evaluate her hypothesis she decides to conduct a 2-year experimental study. She obtains 30 volunteers from undergraduate classes to participate. She randomly assigns an equal number of students to three groups: placebo (group 1), low doses of vitamin C (group 2), and high doses of vitamin C (group 3). In the first and second years of the study, students in all three groups are monitored to assess the number of days that they have cold symptoms, during the first year, students do not take any pills. In the second year of the study, students take pills that contain one of the following: no active ingredients (group 1), low doses of vitamin C (group 2), or high doses of vitamin C (group 3).Once the data was analyzed follow-up tests were conducted to evaluate pair-wise differences among the means.

Tests of Between-Subject Effects
Dependent Variable: DIFF
Source Type III Sum of Squares df Mean Square F Sig. Partial Eta Squared
Corrected Model 205.400 2 102.700 4.836 .016 .264
Intercept 1.200 1 1.200 .057 .814 .002
GROUP 205.400 2 102.700 4.836 .016 .264
Error 573.400 27 21.237
Total 780.000 30
Corrected Total 778.800 29

a R Squared = .264 (Adjusted R Squared = .209)

The test is significant because F (2,27)= .057, p=002.

The test is not significant because F (2, 27)= 4.94, p= .26

The test is significant because F (2,27)=4.84, p=.02.

The test is not significant because F (2,27)=4.84, p= .26

#### Solution Summary

This solution provides step-by-step solutions. The tests of between-subject effects are determined.

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