Seasonal affective disorder (SAD) is a type of depression during seasons with le

Question

Seasonal affective disorder (SAD) is a type of depression during seasons with less daylight (e.g., winter months). One therapy for SAD is phototherapy, which is increased exposure to light used to improve mood. A researcher tests this therapy by exposing a sample of SAD patients to different intensities of light (low, medium, high) in a light box, either in the morning or at night (these are the times thought to be most effective for light therapy). All participants rated their mood following this therapy on a scale from 1 (poor mood) to 9 (improved mood). The hypothetical results are given in the following table. (a) Complete the F-table and make a decision to retain or reject the null hypothesis for each hypothesis test. (Round your answers to two decimal places. Assume experimentwise alpha equal to 0.05.) State the decision for the main effect of the time of day. Retain the null hypothesis Reject the null hypothesis State the decision for the main effect of intensity. Retain the null hypothesis. Reject the null hypothesis. State the decision for the interaction effect. Retain the null hypothesis. Reject the null hypothesis.

Explanation / Answer

R code

Source of Variation

SS

df

MS

F

Time of day

0.69

1

0.69

0.30

Intensity

18.17

2

9.08

3.94

Time of day * Intensity

0.72

2

0.36

0.16

Error

69.17

30

2.31

Total

88.75

35

The 2 way anova model was done using R.

Source of Variation

SS

df

MS

F

Time of day

0.69

1

0.69

0.30

Intensity

18.17

2

9.08

3.94

Time of day * Intensity

0.72

2

0.36

0.16

Error

69.17

30

2.31

Total

88.75

35

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