Dr. Vallerga and Dr. Ligda are interested in the effects of cell-phone use while
ID: 3153121 • 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:
Conduct all six steps of hypothesis testing.
Compute the mean and standard deviation for each group.
Compute Cohen’s d
Answer the following questions using the data and graphs.
Questions (Be sure to use complete sentences):
In this study, what was the independent and dependent variable?
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?
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?
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?
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
answer a)
step1 : define null (H0) and alternative (H1) hypothesis
H0:participants in the Cell-phone group have same driving errors than participants in the Passenger group.
H1:participants in the Cell-phone group would have more driving errors than participants in the Passenger group.
step 2: define alpha level of significance
alpha=0.05
step 3: defince critical value
here we use t-test and critical value= t(0.05,38)=2.02
step 4: define test statistic ,
here we use t-test and t=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))=8.84
step 5: compare test statistics: critical value=2.02 is less than calculated t-value=8.84
step 6: reject null hypothesis
answer part 2)
answer part 3) cohens d= (difference of mean)/standard devitaon=(17.85-10.8)/(5.0465)=1.397
ansewer part 4)
indepependent variable= individuals in a driving simulator
dependent variable=number of driving errors
mean difference=17.85-10.8=7.05 , participants in the Cell-phone group would have more driving errors than participants in the Passenger group.
Yes
What was the standard error of the difference=5.0465/sqrt(40)=0.7979
NO, the standard error smaller than the mean difference
NO, it cannot conclude that cell-phone use causes increased driving errors compared to listening to talk radio, because the above conclustion was to compare between participants in the Cell-phone group and 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 mean= 17.85 10.8 standard deviaion= s= 5.060424363 5.032525786 n= 20 20 sp2= 25.46710526 sp= 5.046494354Related Questions
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