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As part of its "It Can Wait" campaign to discourage texting while driving, AT&T recently released the results of separate surveys concerning the extent of texting while driving among adults twd_commutor_survey and among teens att_teen_survey_executive . In the survey of the adults, 496 of n1 = 1,011 adult drivers (49.06%) said they text while driving. In the survey of the teens, 516 of n2 = 1,200 (43%) said they text while driving.
Question 1. Calculate a 98% confidence interval for the difference padult - pteen in the proportions of adults that text while driving and the proportion of teens that text while driving. (use 4 decimal places in your answers) lower bound upper bound
Be:
X₁: Number of adult drivers that text while driving, out of 1011.
n₁= 1011
x₁= 496
p₁'= 496/1011= 0.4906
X₂: Number of teen drivers that text while driving, out of 1200.
n₂= 1200
x₂= 516
p₂'= 516/1200= 0.43
For the 98% CI for p₁-p₂
[tex]Z_{1-\alpha /2}= Z_{0.99}= 2.326[/tex]
(p₁'-p₂')±[tex]Z_{1-\alpha /2}[/tex] * [tex]\sqrt{\frac{p'_1(1-p'_1)}{n_1} +\frac{p'_2(1-p'_2)}{n_2} }[/tex]
(0.4906-0.43)±2.326*[tex]\sqrt{\frac{0.4906(1-0.4906)}{1011} +\frac{0.43(1-0.43)}{1200} }[/tex]
0.0606±2.326*0.0212
[0.011; 0.11]
Using a 98% confidence level, you'd expect that the interval [0.011; 0.11] contains the difference between the population proportion of adults that text while driving and the population proportion of teens that ext while driving.
Question 2. Choose the correct interpretation of the above confidence interval. Note: 2 submissions allowed.
To decide over a hypothesis test using a confidence interval there are several conditions that should be met:
1) The hypotheses should be two-tailed:
H₀: p₁ - p₂= 0
H₁: p₁ - p₂≠ 0
2) The confidence level of the interval and the significance level of the test should be complementary, this means that if the interval was constructed with a level 1 - α: 0.98 then the test should be made using α: 0.02.
Naturally, the hypotheses and the CI should be made for the same parameters.
If all conditions are met, the decision criteria is as follows:
If the CI contains the value stated in the null hypothesis, the decision is to not reject the null hypothesis.
If the CI doesn't contain the value stated in the null hypothesis, the decision is to reject the null hypothesis.
In this case, the value stated in the null hypothesis is "zero" and is not included in the interval, so the decision is to reject the null hypothesis. You can conclude that the population proportions of adults and teens that text while driving are different.
Considering that the CI is positive, we can think that the proportion of adults that text while driving is grater than the proportion of teens that text while driving.
Options:
1) Since 0 is not in the confidence interval, the surveys provide evidence that the proportion of teens that text while driving is greater than the proportion of adults that text while driving.
2) Since the confidence interval is entirely positive, the surveys provide evidence that the proportion of teens that text while driving is greater than the proportion of adults that text while driving.
3) Since the confidence interval is entirely positive, the surveys provide evidence that the proportion of adults that text while driving is greater than the proportion of teens that text while driving.
4) Since 0 is not in the confidence interval, the surveys provide evidence that there is no significant difference between the proportions of adults and teens that text while driving.
The correct option is: "3"
I hope this helps!
