AP Statistics Choose an Inference Method

The Gallup Poll interviews 1600 people. Of these, 18% say that they jog regularly. The news report adds: “The poll had a margin of error of plus or minus three percentage points at a 95% confidence level.” You can safely conclude that

• 95% of all Gallup Poll samples like this one give answers within ± 3% of the true population value.

• 95% of all Gallup Poll samples like this one give answers within ± 3% of the true population value.

• 95% of all Gallup Poll samples like this one give answers within ± 3% of the true population value.

• we can be 95% confident that the sample proportion is captured by the confidence interval.

• if Gallup took many samples, 95% of them would find that 18% of the people in the sample jog.

In preparing to construct a one-sample t interval for a population mean, suppose we are not sure if the population distribution is Normal. In which of the following circumstances would we not be safe constructing the interval based on an SRS of size 24 from the population?

• A stemplot of the data is roughly bell-shaped.

• A histogram of the data shows slight skewness.

• A boxplot of the data has a large outlier.

• The sample standard deviation is large

• A Normal probability plot of the data is fairly linear.

Many television viewers express doubts about the validity of certain commercials. In an attempt to answer their critics, Timex Group USA wishes to estimate the proportion of consumers who believe what is shown in Timex television commercials. Let p represent the true proportion of consumers who believe what is shown in Timex television commercials. What is the smallest number of consumers that Timex can survey to guarantee a margin of error of 0.05 or less at a 99% confidence level?

• 550

• 600

• 650

• 700

• 750

You want to compute a 90% confidence interval for the mean of a population with unknown population standard deviation. The sample size is 30. The value of t* you would use for this interval is

• 1.645

• 1.699

• 1.697

• 1.96

• 2.045

• A

• B

• C

• D

• E

Suppose we want a 90% confidence interval for the average amount spent on books by freshmen in their first year at a major university. The interval is to have a margin of error of $2. Based on last year’s book sales, we estimate that the standard deviation of the amount spent will be close to $30. The number of observations required is closest to

• 25

• 30

• 608

• 609

• 865

A Census Bureau report on the income of Americans says that with 90% confidence the median income of all U.S. households in a recent year was $57,005 with a margin of error of ±$742. This means that

• 90% of all households had incomes in the range $57,005 ± $742.

• we can be sure that the median income for all households in the country lies in the interval $57,005 ± $742.

• 90% of the households in the sample interviewed by the Census Bureau had incomes in the interval $57,005 ± $742.

• the Census Bureau got the result $57,005 ± $742 using a method that will capture the true median income 90% of the time when used repeatedly.

• 90% of all possible samples of this same size would result in a sample median that falls within $742 of $57,005.

A research company wants to estimate the proportion of people who like oatmeal.  They want the confidence level to be 95%.  The company gets 325 people to sign up for the survey, but on the day that the survey is issued, only 250 people show up and take the survey.  What happens to the confidence interval?

• It gets larger

• It gets smaller

• It stays the same

• Too little information given

Construct a 90% confidence interval of a random sample size of 19 cows with a mean of 155.526 and a standard deviation of 19.993. 

• (146.54, 164.52)

• (147.57, 163.48)

• (147.59, 163.46)

• (143.69, 167.36)

Choose the appropriate confidence interval for the situation: After watching a horror film, 34 out of 50 people reported problems getting to sleep.

• z confidence interval for a mean

• t confidence interval for a mean

• z confidence interval for a proportion

• t confidence interval for a proportion