www.stat.ucla.edu/~dinov/courses_students.dir/08/Fall/STAT13.1.dir/ 1
Stats 13.1 Fall 2008: Homework 6 Solutions
http://www.stat.ucla.edu/~dinov/courses_students.dir/08/Fall/STAT13.1.dir/
1. Problem 1
• Here, we will use a 2-sample T-test to compare the means of 2 independent samples
H0: µ1 - µ2 = 0
HA: µ1 - µ2 ≠ 0
494.0
5
19.7
5
73.8
22.2972.31
)(
0
22
21
21
0=
+
−
=
−
−−
=yySE
yy
T
Now, we compare this to a Students T-distribution with n1 + n2 – 2 = 8 degrees of freedom using SOCR to
find p(T(df=8) > T0 = 0.494) = 0.32
In this case we have a 2-tailed test, and so our p-value is 2*0.32 = 0.64.
Conclusion: We fail to reject the null hypothesis since 0.64>0.10. We conclude that according to our data
the mean weight of thymus glands after being incubated for 14 days is not different than the mean weight after
being incubated for 15 days. In other words, there is no statistically significant mean difference in thymus
glands weights.
• Although the mean weight of thymus glands after 15 days of incubation is lower, this is most likely due to
variability and small sample size.
• Our result matches SOCR 2 independent sample T-test (see figure 1)
