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. Light Intensity Low Medium High Time of Day Morning 5 5 7 6 6 8 4 4 6 7 7 9 4 9 5 6 8 8 Night 5 6 8 8 8 7 6 7 6 7 5 8 4 9 7 2 8 6 (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.) Source of Variation SS df MS F Time of day Incorrect: Your answer is incorrect. Intensity Time of day × Intensity Error Total

Answer 1

	Light Intensity
	Low	Medium	High
Morning	5	5	7
	6	6	8
	4	4	6
	7	7	9
	4	9	5
	6	8	8
Night	5	6	8
	8	8	7
	6	7	6
	7	5	8
	4	9	7
	2	8	6

Anova: Two-Factor With Replication
SUMMARY	Low	Medium	High	Total
Morning
Count	6	6	6	18
Sum	32	39	43	114
Average	5.333333333	6.5	7.166666667	6.333333333
Variance	1.466666667	3.5	2.166666667	2.705882353
Night
Count	6	6	6	18
Sum	32	43	42	117
Average	5.333333333	7.166666667	7	6.5
Variance	4.666666667	2.166666667	0.8	2.970588235
Total
Count	12	12	12
Sum	64	82	85
Average	5.333333333	6.833333333	7.083333333
Variance	2.787878788	2.696969697	1.356060606
ANOVA
Source of Variation	SS	df	MS	F	P-value	F crit
Time of day	0.25	1	0.25	0.101580135	0.752150046	4.17087679
Intensity	21.5	2	10.75	4.367945824	0.021632936	3.3158295
Interaction	1.166666667	2	0.583333333	0.237020316	0.790438685	3.3158295
Error	73.83333333	30	2.461111111
Total	96.75	35