Question

Researchers in mental health fields are often interested in evaluating the effectiveness of using food images to enhance positive mood. Adapting a typical design from such studies, suppose we have participants rate their mood change on a standard self-report affect scale after viewing images of "comfort" foods, fruits/vegetables (F/V), and random non-food images (used as a control group). The results are given in the table at right for this hypothetical study.

Images
Control	F/V	Comfort Foods
0	0	3
1	1	2
1	2	3
3	3	5
0	1	0

(a) Complete the F-table. (Round your answers to two decimal places.)

Source of Variation	SS	df	MS	Fobt
Between groups
Between persons
Within groups (error)
Total

(b) Compute a Bonferroni procedure and interpret the results. (Assume experimentwise alpha equal to 0.05. Select all that apply.)

There were no significant differences between any of the groups.Participants rated a significantly larger mood change after viewing images of fruits/vegetables compared with the mood change after viewing control images.Participants rated a significantly larger mood change after viewing images of comfort foods compared with the mood change after viewing images of fruits/vegetables.Participants rated a significantly larger mood change after viewing images of comfort foods compared with the mood change after viewing control images.

Answer 1

A.

Data Summary from Excel:

ANOVA: Single Factor
SUMMARY
Groups	Count	Sum	Average	Variance
Control	5	5	1	1.5
F/V	5	7	1.4	1.3
Comfort Foods	5	13	2.6	3.3
ANOVA
Source of Variation	SS	df	MS	Fobt	P-value	F crit
Between Groups	6.933333333	2	3.466666667	1.704918033	0.222997177	3.885293835
Within Groups	24.4	12	2.033333333
Total	31.33333333	14

B.

The Bonferroni Correction = *100/(s(s-1)*0.5)

where, s is the no. of groups compared

So,

Bonferroni Correction = 0.05*100/(3(2-1)*0.5)

= 1.66%

Since p-value = 0.223 > 0.0167 i.e. we can't reject H₀.

Interpretation: There were no significant differences between any of the groups.

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