A biopsychologist is studying the role of the role of marijuana (THC) on aggress

Question

A biopsychologist is studying the role of the role of marijuana (THC) on aggression in rats. Specifically, the researcher asserts that the influence of large doses of marijuana will make rats more aggressive. Twenty two rats are randomly assigned to one of two groups. The active ingredient in marijuana is called delta-9 THC. One group of 11 rats serves as a control group and receives a placebo (via injection). A second group of 11 different rats receives a large dose of delta-9 THC via injection. These rats have not been paired up on any trait. Then the researcher tests the animals by recording the number of aggressive responses each of the rats display in a 30 minute test period one hour after the rats were injected. The data are presented below, and represent the number of aggressive responses per rat in each group.

X2 Placebo Group

Complete step 3 of the hypothesis testing procedure and calculate t using which ever formula you prefer. Round to the nearest hundredths place. If your calculated t is not identical to one of the values below, but within plus or minus 0.16 of an answer below, assume it's a rounding error and select the answer that is closest to your calculated value. Ignore the minus sign if your calculated t is negative.

X1
Large dose of delta-9 THC Group

X2 Placebo Group

17 9 15 12 18 11 14 12 20 15 11 12 15 10 20 19 18 14 19 9 12 10

Explanation / Answer

Here x1 = 16.2727

s1 = 3.1013

x2 = 12.0909

s2 = 2.9818

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

= sqrt [(9.6182 + 8.8909)/2 ] = 3.0421

Standard error of difference se0 = sp * sqrt (1/n1 + 1/n2) = 3.0421 * sqrt (1/11 + 1/11)= 1.2972

Test statistic

t = (x1 - x2)/se0 = (16.2727 - 12.0909)/1.2972 = 3.2237

so e is the answer as the correct value of t is not listed in alternatives "a" through "e", even when taking into consideration a rounding error of plus or minus 0.16.

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