A researcher conducts an independent-measures study examining how the brain chem

Question

A researcher conducts an independent-measures study examining how the brain chemical serotonin is related to aggression. One sample of rats serves as a control group and receives a placebo that does not affect normal levels of serotonin. A second sample of rats receives a drug that lowers brain levels of serotonin. Then the researcher tests the animals by recording the number of aggressive responses each of the rats display. The data are as follows. Control (Sample 1) Low Serotonin (Sample 2) n = 10 n = 15 M = 12 M = 15.5 SS = 120.5 SS = 190.0

a. State the Hypotheses in symbols ONLY.

b. Does the drug have a significant effect on aggression? Conduct a hypothesis test for the data. Write your results in two sentences with the outcome of the hypothesis test as presented in a research report. Use an alpha level of .05, two tailed (state the critical value).

c. Measure the effect size and include it in your results write-up.

*You can use the 4 step process for hypothesis testing as your set up to answer the question.

Please solve step by step, and please write in legible writing. Thank you :)

Explanation / Answer

Here the information is given below.

Here S1 = sqrt[SS/n-1] = sqrt [120.5/9] = 3.659

s2 = sqrt [SS/ (n-1)] = sqrt [ 190/14] = 3.684

Here pooled standard deviation sp = sqrt [ {(n-1)s12 + (n-1)s22}/ (n1 + n2 -2)]

s2p = sqrt [ (SS1 + SS2)/ (n1 + n2 -2)] = [ (120.5 + 190)/ (10 + 15-2)] = 13.5

standard error of the difference of mean = sqrt [sp2 * (1/n1 + 1/n2)] = sqrt [ 13.5 * (1/10 + 1/15)] = sqrt(2.25) = 1.5

(a) Step I :

Hypothesis are

H0 : 1 = 2

Ha : 1 2

Step II :

Significance level alpha = 0.05

Step III:

Here critical statistic alpha = 0.05, dF = 10 + 15 -2 = 23

tcritical = t0.05,23 = 2.0687

so we will reject the null hypothesis if l t l > tcritical

Step : 4

Test statistic

t = (M1 - M2 )/ se0 = (12 - 15.5)/ 1.5 = - 2.3333

here

t > tcritical so we shall reject the null hypothesis and can conclude that there is significant difference between population mean.

(3) Effect size = (M1 - M2)/ sp = (15.5 - 12)/ sqrt (13.5) = 3.5/ 3.6742 = 0.9526

here the effect size is high and we can say that the difference is significant too practically.

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