9.4  Test Yourself!
9.4  Test Yourself!Think About It!
Select the answer you think is correct  then click the right arrow to proceed to the next question.
True or False: Since 98/49 = 2, a 98% confidence interval will be twice as wide as a 49% interval.

The answer is False – the change in width due to higher confidence goes with the area under the normal curve not with the level of confidence.

Correct. The change in width due to higher confidence goes with the area under the normal curve not with the level of confidence.
Suppose 100 different polls were taken using the same methodology to construct 90% confidence intervals for the proportion of voters who favor a tax increase to support the school district. Which of the following is true?

Correct. The level of confidence tells you what percentage of time you expect the interval to cover the parameter.

The answer is: About 90 of the polls would have a margin of error that covered the true proportion of voters favoring the tax increase. The level of confidence tells you what percentage of time you expect the interval to cover the parameter.

The answer is: About 90 of the polls would have a margin of error that covered the true proportion of voters favoring the tax increase. The level of confidence tells you what percentage of time you expect the interval to cover the parameter.
The goal of a confidence interval is to suggest possible values for a _________.

Correct. Population value  because once a sample has been obtained there is no mystery about what is the value of the sample estimate. The confidence interval uses sample information, including the sample estimate, to try to infer what would be the value for the entire population.

The answer is population value  because once a sample has been obtained there is no mystery about what is the value of the sample estimate. The confidence interval uses sample information, including the sample estimate, to try to infer what would be the value for the entire population.
Which of the following is the typical structure of a confidence interval?
One hundred and fifty students attend the lecture of a statistics course on the first day of class. The course instructor wants to estimate the average height of the students in the room and asks the nine students in the front row to write down their heights. The average height of these nine students turned out to be 64 inches with a standard deviation of 3 inches. Would it be appropriate to use the formula:
sample average ± 2SEM
to make a 95% confidence statement about the average height of the students in the class based on the data given in the problem?

The answer is: No, because this is not a random sample. The formula here is based on probability results that apply to probability samples not to convenience samples.

The answer is: No, because this is not a random sample. The formula here is based on probability results that apply to probability samples not to convenience samples.

Correct. The formula here is based on probability results that apply to probability samples not to convenience samples.