1. The levels of iron in liver tissue from 12 rats fed on beef and 11 rats on plant oils were
compared using the t-test to see if there was a significant difference at the 5% level. Part
of the table showing the critical values for the t-test is shown below.
Degrees of Freedom
19
20
21
22
23
p= 0.1
1.729
1.725
1.721
1.717
1.714
p=0.05
2.093
2.086
2.080
2.074
2.069
p=0.01
2.861
2.845
2.831
2.819
2.807
p=0.001
3.883
3.850
3.819
3.792
3.767
What is the critical value above which the two samples can be considered significantly
different?
A. 2.086
B. 2.080
C. 2.074
D. 2.069
2. What do error bars on graphs show?
A. If the data is correct or not
B. How variable the data is
C. Which result is closest to the true result
D. What statistical technique was used to eliminate incorrect results
3. What is the relationship between cause and correlation?
A. A correlation does not establish a causal relationship
B. A correlation requires a scientific experiment, while cause does not
C. A correlation requires collection of data, cause does not
D. A causal relationship does not establish a correlation
4. Rice (Oryza sativa) is usually intolerant to sustained submergence under water, although
it grows rapidly in height for a few days before dying. This is true for one variety, Oryza
sativa japonica. The variety Oryza sativa indica is much more tolerant to submergence.
Three genetically modified forms of O. sativa japonica, GMFA, GMFB, GMFC, were
made using different fragments of DNA taken from O. sativa indica. The plants were
then submerged for a period of 11 days. The heights of all the plants were measured at
the beginning and at the end of the submergence period.
(a)
i.
State which group of rice plants were the shortest at the begging of the experiment
ii. Given each sample set contains 15 plants what are the degrees of freedom for
comparing the GMFA group to the control?
iii.
The t-value comparing the GMFA to the control is determine to be t=2.237. Do
we accept or reject the null hypothesis based on this data?
(b) Explain how the error bars can be used to compare the results for O. sativa indica
5. A researcher measures the wing-spans of 12 red-throat and 13 broad-billed
hummingbirds. The t-value was calculated as 2.15. Deduce the significance of the
difference between the two types of birds.
 H0: “There is no significant difference”
 H1: “There is a significant
Degrees of Freedom=______
t=____ critical value=______
Conclusion: There is/is not a significant difference between the results.
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