Dr. Vallerga and Dr. Ligda are interested in the effects of cell-phone use while
ID: 3152738 • Letter: D
Question
Dr. Vallerga and Dr. Ligda are interested in the effects of cell-phone use while driving on the number of driving errors (e.g., running red lights, failing to maintain a safe distance between other cars, slowed reaction time). The researchers tested a sample of 40 individuals in a driving simulator. Participants were randomly assigned to one of two groups of 20 people each. The Cell-phone group talked on the phone (using a hands-free device) and the second group talked with a passenger in the car. The number of driving errors was recorded. The researchers hypothesize that participants in the Cell-phone group would have more driving errors than participants in the Passenger group.
Cell-Phone Group
Passenger Group
13
1
21
16
16
17
12
8
19
9
10
15
12
10
19
11
13
5
28
8
14
6
13
20
16
11
23
7
25
6
20
10
23
8
24
19
17
14
19
15
Summary of Tasks:
a. Conduct all six steps of hypothesis testing.
b. Compute the mean and standard deviation for each group.
c. Compute Cohen’s d
Questions (Be sure to use complete sentences):
1. In this study, what was the independent and dependent variable?
2. Describe the variability in each distribution: What is the standard deviation for each group? What does this measure tell us about the dispersion of scores in each group?
3. What was the mean difference? What does this value tell us about the effects of cell-phone use on driving errors? Was the mean difference in the predicted direction?
4. What was the standard error of the difference? What does this value tell us about how large of a mean difference we would expect to find purely by chance? Is the standard error large than the mean difference?
5. From all of this information, can you conclude that cell-phone use causes increased driving errors compared to listening to talk radio? Explain your answer.
Cell-Phone Group
Passenger Group
13
1
21
16
16
17
12
8
19
9
10
15
12
10
19
11
13
5
28
8
14
6
13
20
16
11
23
7
25
6
20
10
23
8
24
19
17
14
19
15
Explanation / Answer
pooled stanard deviation= sp=5.0465 and sp2=((n1-1)s12+(n2-1)s22)/n and n=n1+n2-2
here n1=20, n2=20 ,
answer a)
step 1: H0:Cell-phone group would have same driving errors as participants in the Passenger group
H1:Cell-phone group would have more driving errors than participants in the Passenger group
step 2: alpha=0.05 (let)
step 3: critical value =t(0.5,38)=2.02
step 4: test statistic= t=(mean1-mean2)/(sp/n1/2) and sp2=((n1-1)s12+(n2-1)s22)/n and n=n1+n2-2
t=(17.85-10.8)/(5.0465/sqrt(40))=8.83
step 5: comparing the t statistic 8.83 with critical t=2.1 ,
t-statistic > critical t
step 6: conclusion reject null hypothesis and conclude that Cell-phone group would have more driving errors than participants in the Passenger group
answer c) cohen d=(mean1-mean2)/sp=(17.85-10.8)/(5.0465)=1.397
Cell-Phone Group Passenger Group 13 1 21 16 16 17 12 8 19 9 10 15 12 10 19 11 13 5 28 8 14 6 13 20 16 11 23 7 25 6 20 10 23 8 24 19 17 14 19 15 mean= 17.85 10.8 standard deviaion= s= 5.060424363 5.032525786 n= 20 20Related Questions
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