Psychology 2801
Practice Exam Answers
1) A researcher would like to test the effectiveness of a newly developed growth hormone. The
researcher knows that under normal circumstances laboratory rats reach an average weight of μ = 950
grams at 10 weeks of age. The distribution of weights is normal with
σ
= 30. A random sample of 30
newborn rats is obtained, and the hormone is given to each rat. When the rats in the sample reach 10
weeks old, they are weighed. The mean weight for this sample is 974 grams with a standard deviation
of 27. The researcher wants to know if this sample of 30 rats differs from the general population.
a) Test this hypothesis using an
α
of .05.
H
0
: μ = 950
H
1
: μ
≠
950
4.38
=
−
=
30
30
950
974
z
z
crit
using an
α
of .05 is ±
1.96
z
obt
> z
crit
Since
z
obt
(4.38)
> z
crit
(1.96), I reject the null that this sample of rats came
from the general population. Since the mean for this sample (974) was higher, there was
some evidence that these rats scored higher than the general population.
2) To test the effectiveness of a new treatment for depression, a sample is selected from a population
with μ = 40. After the treatment is administered to the individuals, the sample mean equaled 46 and
the standard deviation equaled 12. The researcher is interested in whether the drug will affect
depression scores over time.
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 Spring '08
 GUYER
 Psychology, Normal Distribution, Standard Deviation, Null hypothesis, researcher

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