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.

State the decision for the main effect of intensity.

State the decision for the interaction effect.

(b) Compute Tukey's HSD to analyze the significant main effect.

Summarize the results for this test using APA format.

This answer has not been graded yet.

Light Intensity Low Medium High Time of
Day Morning 5 5 7 6 6 8 4 4 6 7 7 9 5 9 5 6 8 8 Night 5 6 9 8 8 7 6 7 6 7 5 7 4 9 7 3 8 6

Explanation / Answer

ANOVA Source of Variation SS df MS F P-value F crit Time of Day 0.25 1 0.25 0.11 0.74 4.17 Intensity 17.39 2 8.69 3.83 0.03 3.32 Time of Day * Intensity 1.17 2 0.58 0.26 0.78 3.32 Error 68.17 30 2.27 Total 86.97 35 Time of Day Since calculated F is lower than F crit, we retain the null hypothesis. Intensity Since calculated F is greater than F crit, we reject the null hypothesis and accept alternate hypothesis. Time of Day * Intensity (Interaction effect) Since calculated F is lower than F crit, we retain the null hypothesis.

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