Download Practice Quiz 4

Psy 210 Fall 2004
Practice Quiz 4
Thurs Nov 18, 2004
Instructor: Kim Barchard
1. According to Dr. Barchard, if you believe the null hypothesis and you retain it, you should
(1 mark)
a) say you accept the null hypothesis
b) say you reject the alternative hypothesis
c) calculate a confidence interval
d) design a new study with lower power
2. Give an example of a null hypothesis that some researchers might believe. Write your
hypothesis in words, rather than symbols, so it is clear what variables and participants you
are talking about. (1 mark)
3. Which of the following statements about power is true? (1 mark)
a) We can calculate Beta exactly
b) SPSS will not estimate power, but other programs will
c) Power is usually around .6 or .7
d) The symbol for power is Beta
e) The symbol for power is p
4. If you are conducting a z-test for the hypothesis that the population mean is 100, and you
have a sample size of 101, what is your critical value if you use alpha = .10 and a one-tailed
test? (1 mark)
5. Imagine that a researcher believes that a group of children is extremely extraverted. The
population mean for extraversion is 50. What would the alternative hypothesis be
If a one-tailed test was used? (1 mark)
If a two-tailed test was used? (1 mark)
6. The advantage of one-tailed tests over two-tailed tests is (1 mark)
a) they have more power
b) they use larger values for alpha
c) they result in smaller standard errors
d) more than one of the above is an advantage of one-tailed tests
7. When should you use the t-test rather than the z-test? (1 mark)
8. If a one-tailed test with alpha = .05 is used, which critical value is higher, the one for the
z-test or the one for the t-test? (1 mark)
a) z-test
b) t-test
c) the critical values will be the same
9. Confirm or disconfirm the following claim: “As sample size increases, the t-distribution
approaches the normal distribution. In practical terms, what this means is that as sample size
increases, the critical values from the t-distribution become closer and closer to the critical
values from the normal distribution.” Confirm or disconfirm this claim by looking for the
critical value for a two-tailed test, using alpha = .05, in two ways. First, find this critical
value using the normal table. Second, find this value by looking in the t-tables, using an
infinite number of degrees of freedom.
Critical Value using z-table:
Critical Value using t-table:
Circle one:
a) Confirm
b) Disconfirm
10. According to lecture, why do most statistics textbooks say that you should not say you
“accept” the null hypothesis? (1 mark)
11. Imagine that Jason was conducting an honors thesis on learning in older adults. Imagine that
adults in general get an average of 62 on this test of learning. In his sample of 51 older
adults, the sample mean was 59 and the sample standard deviation was 15. Test the research
hypothesis that older adults have lower than average learning scores, using a one-tailed test
with alpha = .05. Show all your work or you won’t get full marks. (7 marks)
12. A 68% confidence interval for the mean is given by the interval [3, 5]. If you wanted to use
this interval to do hypothesis testing, what would alpha be? (1 mark)
13. A 95% confidence interval for the mean is given by the interval [12, 26]. If a researcher
conducted a two-tailed test, using alpha .05, of each of the following hypotheses, would they
retain or reject that hypothesis? (1 mark each)
Ho: mu = 5
Ho: mu = 10
Ho: mu = 12
Ho: mu = 20
Ho: mu = 25
Ho: mu = 26
Ho: mu = 30
14. Dr. Raza thinks that cats are not as smart as dogs. Dr. Raza tests 36 cats, using Dr. Stanley
Coren’s intelligence test for dogs. That test is known to have a mean of 100 and a standard
deviation of 15. The 36 cats have a sample mean of 85. Calculate a 90% confidence interval
for the population mean. (5 marks)
15. The z-test and t-test both assume independence. What are we assuming is independent of
what? (1 mark)
16. The z-test and the t-test both assume normality. What are we assuming has a normal
distribution? (1 mark)
17. The z-test and the t-test both assume normality. When can we violate this assumption?
(1 mark)
a) Never
b) When sample size is less than 30
c) When sample size is 30 or more
d) When we know the population standard deviation
18. Confidence intervals for the population mean assume independence. When can we violate
this assumption? (1 mark)
19. Consider the following data. A study is being conducted to examine the effectiveness of a
weight-loss program. The weight of each participant is measured before and after being on
this program for 6 months. What statistical technique can be used to test the effectiveness of
this program? (1 mark)
a) one-sample z-test
b) one-sample t-test
c) independent sample t-test
d) dependent sample t-test
e) none of the above