Chapter 9: Estimation and Confidence Intervals - SmartBook
From a random sample of 20 adults, five indicate that they regularly read books. What is the sample proportion?
0.25
If there is no estimate of the population proportion, what value should be used?
0.5
If there is no estimate of the population proportion, what value should be used? Multiple choice question.
0.5
Calculate a 95% confidence interval for a sample mean of 20 with a sample standard deviation of 10 and a sample size of 9. The answer should be accurate to the nearest decimal.
12.31 to 27.69
Suppose you want to estimate the population mean with 99% confidence with a margin of error of 2.5. If the estimate of the population standard deviation is 11, what sample size is required?
129 Reason: n=(2.58*11/2.5)^2
Calculate a 90% confidence interval for a sample mean of 15 with a sample standard deviation of 5 and a sample size of 25. The answer should be accurate to the nearest decimal.
13.29 to 16.71
A sample of size 16 is taken from a population with standard deviation 8. The sample mean is 22. Which of the following is a 95% confidence interval for the population mean?
18.08 to 25.92
What z-value is used to construct a 98% confidence interval for the population mean when the population standard deviation is known?
2.33 Reason: 0.9800/2=0.4900; z=2.33⇨0.4901
A large jar contains a mixture of white and black beans. In a randomly chosen handful of 120 beans 40 were black. Create a 98% confidence interval for the proportion of black beans in the jar. Express your answer to the nearest percent.
23% to 43%
A large jar contains a mixture of white and black beans. A small sample of beans was found to be 1/4 black beans. What size sample would be needed to estimate the proportion of black with an error of no more than 0.05 and a confidence level of 95%
289 Reason: n=0.25(0.75)*(1.96/0.05)^2
A sample of size 25 is taken from a population with standard deviation 6. The sample mean is 10. Which of the following is a 99% confidence interval for the population mean?
6.9 to 13.1
Suppose you would like to estimate what proportion of students work full-time. If you have no estimate of the population proportion, what sample size would be needed to estimate the proportion with an error of no more than 0.04 and a confidence level of 95%?
601 Reason: n=0.5(0.5)*(1.96/0.04)^2
Suppose you want to estimate the population mean with 95% confidence with a margin of error of 2. If the estimate of the population standard deviation is 8, what sample size is required?
62 Reason: n=(1.96*8/2)^2
Suppose that, after using the sample size formula, you find n=83.25. What sample size should you use?
84 Reason: Yes, always round UP.
A student found that out of 100 cars that passed an intersection 20 were Toyotas. Create a 95% confidence interval for the population proportion of Toyotas.
0.12 to 0. 28
A proportion would be especially useful in which one of the following cases?
Estimating the percentage of students who have full-time jobs. Reason: Proportions work great for nominal data.
In constructing a confidence interval to estimate the population mean from a sample, which of the following steps are necessary only when σ is not known? Select all that apply.
Find the t-value for the proper distribution, based on the sample size. Find the sample standard deviation.
Which of the following statements correctly describe the role of the population standard deviation, σ, in creating a confidence interval for the population mean? Select all that apply.
If σ is not known, we estimate it using the sample standard deviation, s. If σ is known, we use it to calculate the confidence interval.
When we want to estimate the mean of a population using a sample, but do not know the population standard deviation, which of the following steps are required? Select all that apply.
Use the t-distribution instead of the Standard Normal to find the confidence interval. Use the sample standard deviation as an estimate of the population standard deviation.
The binomial conditions must be met before we can develop a confidence interval for a population proportion. Which two of the following are binomial conditions?
We can define two outcomes, success and failure. The probability of success is the same for all trials.
Which of the following must be true so that the standard normal distribution can be used to construct a confidence interval for the population proportion?
nπ≥5 and n(1-π)≥5
In creating a confidence interval for the population mean, if σ is unknown, we estimate it using which of the following?
s
When the population standard deviation is know, the confidence interval for the population mean is based on the:
z-statistic
Which of the following considerations require a larger sample size? Select all that apply.
A higher level of confidence. A smaller margin on error.
What is a Confidence Interval? Choose the best description.
A range of values, created using a sample, within which a population parameter has a certain probability of occurring. Reason: E.g. P(a<x<b) = 0.95
Which of the following statements is the best definition of a point estimate?
A sample statistic that estimates a population parameter. Reason: I.e. a single item (point) of information.
When we speak of an "80% confidence level," what are we referring to?
An 80% probability that a parameter will be within a specified interval. Reason: I.e. P(a<x<b) = 0.8
Identify which of the following are traits that apply to the meaning of "proportion." Select all that apply.
It can refer to either a sample or a population. It refers to a fraction, ratio, or percent.
Why is it important to know the population standard deviation when estimating the population mean?
Knowing σ lets us use the standard normal distribution to construct a confidence interval.
How does sample size affect the width of the confidence interval for the population mean?
Larger sample sizes result in narrower intervals.
How does the standard deviation of the population affect the width of the confidence interval for the population mean?
Larger values of the population standard deviation result in wider intervals
Which of the following is the best point estimate of the population mean, μ?
Reason: This is the sample mean. It is a statistic that estimates the population mean.
What should you do if your calculation for appropriate sample size gives a fractional number?
Round up to the next whole number.
For a given confidence level, how does a confidence interval calculated using the t-value compare to one calculated using the z-value?
The confidence interval from the t-value is wider.
What is the difference between the a confidence interval and the level of confidence?
The confidence interval is a range of values, the level of confidence is the probability for that range of values.
Which of the following items are valid considerations in the choice of sample size? Select all that apply.
The desired level of confidence. The population dispersion. The margin of error the researcher will tolerate.
In choosing a sample size for a study, we need to know the population standard deviation. Which of the following could be used to estimate the population standard deviation? Select all that apply.
The population standard deviation from a comparable study. The sample standard deviation from a pilot study.
What is meant by the term "level of confidence"?
The probability that a parameter will be found within the confidence interval. Reason: For example P(a<x<b).
Knowing the population standard deviation allows us to choose an appropriate sample size for a study. Which two of the following could be used to estimate the population standard deviation?
The sample standard deviation from a pilot study. One sixth of the population range.
Which of the factors listed below determine the width of a confidence interval? Select all that apply.
The size of the standard error. The chosen level of confidence.
For a specific confidence level how do the t-value and the z-value compare?
The t-value is larger than the z-value.
If we are estimating the population mean using a sample, under what circumstances would we use the t-distribution?
When we don't know the population standard deviation.
