1. The times for untrained rats to run a standard maze have an N (65, 15) distribution where the times are measured in seconds. The researchers hope to show that training improves the times, and they will do so by testing statistical hypotheses. The appro
Ha : � < 65
This is correct. The alternative hypothesis corresponds to what the researchers are trying to show. If training improves the times, the mice should run the maze in less time so that the mean will decrease. Text reference: pages 372-374 in Chap
2. A social psychologist reports that "in our sample, ethnocentrism was significantly higher (P
if there is actually no difference in ethnocentrism between church attendees and nonattendees, the chance that we would observe a difference as large or larger than we did is less than 5%.
This is correct. Recall that the P-value is the probability comput
3. A researcher wants to know if the average time in jail for robbery has increased from what it was several years ago when the average sentence was 7 years. He obtains data on 400 more recent robberies and finds an average time served of 7.5 years. If we
0.0004
This is correct. The test statistic is = Since the question was whether average time served has increased, the P-value of the test is the area under the standard Normal curve above 3.33. From Table A, this is 0.0004. Text reference: pages 374-378 i
4. The distribution of times that a company's service technicians take to respond to trouble calls is Normal with mean � and the standard deviation ? = 0.25 hours. The company advertises that its service technicians take an average of no more than 2 hours
0.0228.
5. In comparing students who have transferred to my university from a junior college in the area, I want to know if the transfer students do as well as those who enter the university straight from high school. My alternate hypothesis is Ha : �transfer < �
Reject H0 � transfer students do not do as well as those admitted from high school.
6. What is the P-value for a test of the hypotheses H0: � = 10 against Ha: � ? 10 if the calculated statistic is z = 2.56?
0.0104
This is correct. The P-value for the test against Ha: � ? 10 is the area under the standard Normal curve above 2.56 and below -2.56. This is twice the area below -2.56 by symmetry, so p = 2(0.0052) = 0.0104. Text reference: pages 378-382 in Chapter
7. A researcher wants to know if tougher sentencing laws have had the desired impact in terms of deterring crime. He plans to select a sample of states which have enacted a "3 strikes" law and compare violent crime rates before the law was enacted and two
H0 : �before = �after and Ha : �before > �after
This is correct. If the laws have deterred crime, the crime rates will have gone down, and the mean crime rate should be less after the new laws than before. Text reference: pages 372-374 in Chapter 15.
8. Many times the results of a statistical test will be reported as "P level is 1% (remember, the researcher gets to set ), what decision would be made if that's all we know?
You couldn't tell without more information.
9. I have computed a 95% confidence interval for the mean, �, of a population as (13, 20). Based on this interval, we can say
Both choices are true.
10. Suppose we are testing the null hypothesis H0 : � = 50 and the alternative Ha : � ? 50 for a Normal population with ? = 6. The 95% confidence interval for the mean is (51.3, 54.7). Therefore,
the P-value for the test is less than 0.05.