Question

1. A psychologist is interested in investigating whether people who never owned a pet are happier after getting a pet. A questionnaire about their level of happiness is administered to a group of 20 to 29 year-olds when they before they get a pet and after they get a pet. The data are below. (11 points)

Before Pet	After Pet
10	15
9	9
11	10
11 5 9	19 17 15

1. Calculate a t-statistic to compare the happiness levels before and after getting a pet. The variance for the difference scores is s_D² = 24. Show your work. (3 points)

2. Assume that the psychologist uses an  =.05, two-tailed, df = (6-1) = 5. The t_{critical value} = +2.57 and the p-value associated with their t-test statistic was p = .055. Should the psychologist reject or fail to reject the null hypothesis, and why? (2 point)

3. Calculate the estimated Cohen’s d to measure the effect size for this study. (1 point)

4. Interpret your results as if you were reporting them for a journal article. Use APA style. (5 points)

Answer 1

(a)

Before Pet	After Pet	Difference
10	15	-5
9	9	0
11	10	1
11	19	-8
5	17	-12
9	15	-6
	Mean	-5
	Standard	4.89897949
	n	6
	t	-2.5

The test statistic is -2.5.

(b) The p-value is 0.055.

Since the p-value (0.055) is greater than the significance level (0.05), we cannot reject the null hypothesis.

(c) Cohen's d =5/4.89897949 = 1.02

(d) Since the p-value (0.055) is greater than the significance level (0.05), we cannot reject the null hypothesis.

Therefore, we cannot conclude that people who never owned a pet are happier after getting a pet.