Chapter 8

Question 1

Which of the following choices are assumptions that must always be satisfied for a z-test?

a. the participants in the sample must be independently selected
b. The sample size must be ≥ 30
c. none of the other answers is correct
d. the DV must be normally distributed

Answer 1

a. the participants in the sample must be independently selected

Question 2

A grade 6 teacher wanted to know how well the students in her class who have just moved into the school district perform relative to students who began in grade K. She administers a standardized test with a known population mean of 50 and standard deviation of 10. Her class has 20 new and 15 long-term students. Their average score is 55 for the new students and 58 for the long-term students.
A z-test can answer her question.

Answer 2

False

Question 3

Conceptually, all hypothesis tests involve determining the ratio of (observed difference)/(difference due to chance). In a z-test the observed difference is______ and the difference due to chance is_________.

a. Observed: M-μ; Chance: σM
b. Observed: M; Chance: sM
c. Observed: M-μ; Chance: sM
d. Observed: μ; Chance: σM

Answer 3

a. Observed: M-μ; Chance: σM

Question 4

Psychologist Haydn tests the hypothesis that plants exposed to Mozart grow better than other plants. His Mozartian plants grow an average of 3 inches and his control plants are known to grow an average of μ=2.25 inches. His obtained z is +2.68 which is in the critical rejection region. He therefore rejects the null hypothesis. Which of the following is true?

a. He concludes that plants exposed to Mozart grow better than other plants
b. He concludes that plants exposed to Mozart grow less well than other plants
c. He concludes that there is no evidence to support the hypothesis that plants exposed to Mozart grow more rapidly
d. He concludes that there is no difference between plants exposed to Mozart and “normal” plants

Answer 4

a. He concludes that plants exposed to Mozart grow better than other plants

Question 5

When my z-test test concludes that a highly significant difference was observed, which of the following is(are) true?

a. the p value was small
b. the p value was large
c. the absolute value of z observed was large
d. the sample was large
e. the α was large

Answer 5

a. the p value was small
c. the absolute value of z observed was large

Question 6

If you reject the null hypothesis in a non-directional z test, you are concluding that:

a. the sample probably is from the known population
b. the sample is probably NOT from the known population
c. the sampling standard deviation is probably different from the population standard deviation
d. the sampling standard deviation is probably NOT different from the population standard deviation

Answer 6

b. the sample is probably NOT from the known population

Question 7

If you retain the null hypothesis in a non-directional z test, you are concluding that

a. the sampling standard deviation is NOT different from the population standard deviation
b. the sample is NOT different from the reference population
c. the sample is different from the reference population
d. the sampling standard deviation is different from the population standard deviation

Answer 7

b. the sample is NOT different from the reference population

Question 8

One study found a difference between means that was significant at the .05 level. Another study just like the first one failed to reject the null hypothesis. What can you conclude?

a. All of the other answers are correct
b. Something must have gone wrong in the second study
c. This is a failure to replicate and will happen in 5% of possible samples
d. The second study should have found a difference 5% bigger

Answer 8

c. This is a failure to replicate and will happen in 5% of possible samples

Question 9

For a non-directional test with α = .01, what is the critical z?

a. 1.64
b. 2.57
c. 2.32
d. 1.96

Answer 9

b. 2.57

Question 10

Which of the following is an appropriate alternative hypothesis in a directional z test?

a .none of the other answers is correct
b. the obtained sample mean comes from a population with a mean greater than the reference population
c. the obtained sample mean is from a different population than the reference population mean
d. the obtained sample mean is from the same population as the reference population mean

Answer 10

b. the obtained sample mean comes from a population with a mean greater than the reference population

Question 11

A z-test compares a sample to a standard population, by finding the probability of the population mean in a sampling distribution of means based on the sample statistics.

Answer 11

False

Question 12

If the obtained z is 1.87 and the critical z is 1.96 in a non-directional test with α=.05, you would:

a. reject the null hypothesis
b. retain (fail to reject) the null hypothesis
c. conclude that the experiment is improperly done
d. conclude that the effect of the independent variable is real

Answer 12

b. retain (fail to reject) the null hypothesis

Question 13

SpongeBob is trying to optimize the time it takes to make a Krabby Patty. He knows as a baseline that the average time the general population will wait for a fast food item is 100 seconds with standard deviation of 16. He finds that 64 Krusty Krab patrons leave after waiting 95 seconds with a standard deviation of 8.
A z test could assess whether Krusty Krab patrons are more impatient than the general public.

Answer 13

True

Question 14

A psychologist wonders how her new smoking cessation program will compare to the standard program. She measures the number of cigarettes smoked in a week after the new program and compares it to the (known) population mean for the standard program. She decides to use a non-directional test. What is her alternative hypothesis?

a. μNew < μStandard
b. μNew ≤ μStandard
c. μNew = μStandard
d. μNew ≠ μStandard

Answer 14

d. μNew ≠ μStandard

Question 15

A rental car company claims the mean time to rent a car on their website is 60 seconds with a standard deviation of 30 seconds. A random sample of 36 customers who attempted to rent a car on the website are surveyed and 30 of them said it took less than 60 sec.

This is enough evidence do a z-test of the companies claim.

Answer 15

False

Question 16

When I say “µ1 ≠ µ2” I am stating:

a. the alternative hypothesis for a directional test
b. the alternative hypothesis for a nondirectional test
c. the null hypothesis for a directional test
d. the null hypothesis for a nondirectional test

Answer 16

b. the alternative hypothesis for a nondirectional test

Question 17

With a critical z of 1.96, which of the following obtained z’s will permit us to reject the null hypothesis?

a. 0.95
b. 0.01
c. 2.56
d 0.75

Answer 17

c. 2.56

Question 18

Which of the following conditions could lead to a significant z-test decision with a small effect size?

a. if the sample is small and the standard error is large
b. sample is small, and the test is non-directional
c. the test is directional and the α is large
d. if the sample is large and α is large

Answer 18

c. the test is directional and the α is large
d. if the sample is large and α is large

Question 23

Which is the best way to report the effect size in an APA report?

a. The effect size, Cohen’s d=.83 was small, indicating the difference was functionally meaningful
b. The effect size, Cohen’s d=.15 was small, indicating the difference was not significant
c. The effect size, Cohen’s d=.83 was large, indicating the difference was functionally meaningful
d. The effect size, Cohen’s d=.15 was large, indicating the difference was functionally meaningful

Answer 23

c. The effect size, Cohen’s d=.83 was large, indicating the difference was functionally meaningful

Question 24

A health communication researcher wondered if people who hear public service announcements made by celebrity spokespersons about the need for mental health screening would develop more positive attitudes about participating in a screening. He randomly selected 64 research participants and developed announcements made by celebrities known to be popular with the participants. From previous attitudinal research, it was known that the mean attitude toward mental health screening among people who hear public service announcements from non-celebrities is 3.5 (on a scale where 0 is a very negative attitude and 10 is positive), with a standard deviation of 2.4. After viewing the announcements by celebrities, the observed sample mean attitude was 4.4 with a standard deviation of 1.6.
The research question is whether public health announcements improve mental health.

Answer 24

False

Question 25

In order to answer the researcher’s question, the hypothesis test should be directional.

Answer 25

True

Question 26

The null hypothesis is M Announcement < μPopulation

Answer 26

False

Question 27

The alternative hypothesis is μCelebrity Announcement > μPopulation

Answer 27

True

Question 28

The researcher decides to use α=.01 to test the hypothesis.
So, the zCrit= 1.645.

Answer 28

False

Question 29

The decision rule for this hypothesis test is: Reject H0 if zObserved ≥ 2.325

Answer 29

True

Question 30

What is the value of the standard error?

Answer 30

0.3

Question 31

What is z Observed?

Answer 31

3

Question 32

The decision is

a. reject H0
b. do not reject H1
c. do not reject H0
d. H1 is true

Answer 32

a. reject H0

Question 33

The effect size for this test is Cohen’s d=

Answer 33

0.375

Question 34

The researcher writes the following first sentence for an APA report:

A z test revealed that 64 participants who heard public health messages from celebrities about the importance of mental health screening had attitudes about mental health (M=4.4) higher than the general population who hears messages from non-celebrities (μ=3.5), z = 3.0, p < .01.
Which of the following are errors in the report?

a. zCrit is not reported
b. the reported p level is incorrect relative to the α level and directionality
c. the significance/non-significance is not reported explicitly
d. the directionality of the test is not reported

Answer 34

c. the significance/non-significance is not reported explicitly
d. the directionality of the test is not reported

Question 35

The researcher writes the following second sentence for the APA report:
The effect size was large (Cohen’s d=.473), indicating the difference was not functionally meaningful.
Which of the following are errors in the report?

a. the functional impact statement is not consistent with the reported Cohen’s d
b. the significance level is not reported
c. the categorization of the effect size does not match the given value of Cohen’s d
d. α level is not correct

Answer 35

a. the functional impact statement is not consistent with the reported Cohen’s d
c. the categorization of the effect size does not match the given value of Cohen’s d