Question

2) How does the neurotransmitter serotonin influences aggression? A researcher conducts a study examining how the brain chemical serotonin is related to aggression. Two samples were collected; one sample serves as the control group which will not receive any treatment drug, the second sample receives a drug that affects serotonin and thus influences aggression. The researcher finally tests the animals by recording the number of aggressive responses. The following results were reported:

Treatment group (serotonin affected):              Control group:

Rat 1 = 12                                                        Rat 5 = 5

Rat 2 = 11                                                        Rat 6 = 6

Rat 3 = 13                                                        Rat 7 = 8

Rat 4 = 8                                                          Rat 8 = 7

Step 1: State your null and alternative hypothesis

Step 2: State your critical value. What is your alpha level? What are your degrees of freedom? (Watch out because you have two samples!) Would this be one-tail or two-tailed?

Step 3: Compute the appropriate statistic for an obtained score (this would also require a mean and standard deviation for each sample)

Step 4: Make your decision, would you reject or fail to reject the null hypothesis? What is your conclusion?

- Should you compute effect size? If so, do it! (3 points) Of course, you should also report the appropriate proportion of variability

Write a formal paragraph to interpret your results (5 points)

Answer 1

1. The hypothesis being tested is:

H₀: µ₁ = µ₂

H₁: µ₁ ≠ µ₂

This is a two tailed test.

2. The critical values are -2.447 and 2.447.

The level of significance is 0.05.

df = 4 + 4 - 2 = 6

3. The test statistic is 3.576.

4. The p-value is 0.0117.

Since the p-value (0.0117) is less than the significance level (0.05), we can reject the null hypothesis.

Effect size = 2.53

This is a large effect.

r² = 0.68

This is a medium effect.

5. Therefore, we can conclude that the drug influences aggression.

Treatment	Control
11.00	6.50	mean
2.16	1.29	std. dev.
4	4	n
	6	df
	4.500	difference (Treatment - Control)
	3.167	pooled variance
	1.780	pooled std. dev.
	1.258	standard error of difference
	0	hypothesized difference
	2.447	critical value
	3.576	t
	.0117	p-value (two-tailed)
	2.53	effect size
	0.68	r²