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The Wall Street Journal reported that the average amount of time that a French p

ID: 3156626 • Letter: T

Question

The Wall Street Journal reported that the average amount of time that a French person spends eating lunch at a restaurant is 22 minutes. Perform a hypothesis test to determine if a difference exists between the average time an American spends eating lunch and the average time a person from France spends eating lunch. The following data represent the time, in minutes, that random French and American diners spent at lunch. Assume that the population variances are equal.

If Population 1 is defined as French diners and Population 2 is defined as American diners, which one of the following statements is true?

Because the 90% confidence interval does not include zero, you can conclude that the average time an American spends at lunch equals the average time that French diners spend at lunch. Because the 90% confidence interval does not include zero, you can conclude that the average time an American spends at lunch differs from the average time that French diners spend at lunch. Because the 90% confidence interval includes zero, you can conclude that the average time an American spends at lunch differs from the average time that French diners spend at lunch. Because the 90% confidence interval includes zero, you cannot conclude that the average time an American spends at lunch differs from the average time that French diners spend at lunch.

Explanation / Answer

> tt <- read.csv("clipboard",header=TRUE,sep=" ")
> tt
American French
1 21 24
2 17 18
3 17 20
4 20 28
5 25 18
6 16 29
7 20 17
8 16 NA

> t.test(tt$American,tt$French,var.equal=TRUE,conf.level=.9)

Two Sample t-test

data: tt$American and tt$French
t = -1.4155, df = 13, p-value = 0.1804
alternative hypothesis: true difference in means is not equal to 0
90 percent confidence interval:
-6.7532752 0.7532752
sample estimates:
mean of x mean of y
19 22

From the above output, the fourth statement is valid, that is, :

Because the 90% confidence interval includes zero, you cannot conclude that the average time an American spends at lunch differs from the average time that French diners spend at lunch.
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