Confidence Intervals

In inferential statistics, what is the term for a single number computed from a sample that is used to estimate a population parameter?

What is the primary purpose of a confidence interval in statistics?

A random sample of 36 scores from a standardized exam is taken. The sample mean is 68, and the population standard deviation is known to be 3. What is the 90 percent confidence interval for the true population mean exam score?

How does increasing the confidence level from 90 percent to 99 percent affect the width of a confidence interval, assuming the sample size and standard deviation remain constant?

What is the primary reason for using the Student's t-distribution instead of the normal distribution when calculating a confidence interval?

A study of hypnotherapy measures the hours of sleep for 12 subjects. The sample mean is 8.9 hours and the sample standard deviation is 1.4 hours. Construct a 95 percent confidence interval for the mean number of hours slept.

In a survey of 500 accounts, a financial officer finds that 300 are more than 30 days overdue. What is the point estimate for the true proportion of accounts receivable that are more than 30 days overdue?

What conditions must be met to use the normal distribution to approximate the binomial distribution when creating a confidence interval for a population proportion?

A poll of 600 students finds that 480 are against new school uniform legislation. What is the 90 percent confidence interval for the true proportion of students who are against the legislation?

When calculating the required sample size for a population proportion, if no prior information about the sample proportion (p') is available, what values are typically used for p' and q' to ensure a sufficiently large sample size?

A researcher wants to estimate the mean weight of newborn elephants. If the population standard deviation is known to be 15 pounds, how many newborn elephants must be weighed to be 95 percent confident that the sample mean is within 4 pounds of the population mean?

What is the relationship between the Student's t-distribution and the standard normal distribution?

The 'Error Bound for a Population Proportion' (EBP) depends on all of the following EXCEPT:

A sample of 80 students is surveyed, and the average amount spent on a spring break trip is 593.84 dollars, with a sample standard deviation of 369.34 dollars. What is the 92 percent confidence interval for the population mean?

What does a 95 percent confidence level imply?

For a confidence interval based on the Student's t-distribution, the degrees of freedom are calculated as:

How will the confidence interval for a population mean change if the sample size is decreased from 100 to 25, keeping all other factors constant?

In a sample of 300 students, 68 percent said they own an iPod and a smartphone. Compute a 97 percent confidence interval for the true percent of students who own both devices.

The term (1 - alpha) represents the:

What is the formula for the sample size needed to estimate a population proportion to within a certain margin of error (e) and confidence level?

A confidence interval is constructed for a population mean, and its range is (50, 70). What is the point estimate of the mean?

Which of the following is NOT a property of the Student's t-distribution?

A poll for a presidential candidate shows they have 40 percent of the vote. The confidence interval is calculated with a margin of error of 3 percentage points. What is the confidence interval?

A confidence interval for a population mean is (67.02, 68.98). What is the error bound for the mean (EBM)?

A mobile phone company wants to determine the percentage of customers who will upgrade. How many customers should be surveyed to be 90 percent confident that the estimated proportion is within three percentage points of the true population proportion?

Which distribution is used to calculate a confidence interval for a single population proportion, provided the sample size is large enough?

The statement 'We are 95 percent confident that the true population mean is between 1.8 and 2.2' means that:

In the formula for a confidence interval for a mean when sigma is unknown, mu ± t * (s/sqrt(n)), what does the 't' value depend on?

A sample of 25 chairs has an average cost of 100 dollars and a sample standard deviation of 50 dollars. What is the 92 percent confidence interval for the population mean cost?

Why must the analyst's desired level of confidence be pre-set and not subject to revision as a result of the calculations?

The general form of a confidence interval for a single population mean, when the population standard deviation is known, is given by:

If a confidence interval is calculated to be (10, 30), what is the error bound (EBM)?

In a survey of 250 people, 98 reported owning a tablet. The 95 percent confidence interval for the true proportion of people who own tablets is approximately:

What is alpha (α) if the confidence level (CL) is 98 percent?

An internet marketing company wants to be 90 percent confident that their estimated proportion of customers who click on ads is within five percentage points of the true proportion. What is the minimum sample size required?

A confidence interval for the population proportion of dogs that compete in professional events is (0.08, 0.16). What is the sample proportion (p')?

The use of the Student's t-distribution for confidence intervals assumes that the underlying population of individual observations is:

If a 95 percent confidence interval for a population mean is (142.92, 159.08), what does this signify?

Which of the following would produce the narrowest confidence interval for a population mean?

Who is credited with discovering the Student's t-distribution while working at the Guinness brewery?

The sample mean is 36 minutes, the population standard deviation is 6 minutes, and the sample size is 28. What is the Error Bound for the Mean (EBM) for a 90 percent confidence interval?

A confidence interval is a random variable because:

In a study of 10 industrial stocks, the average EPS was 1.85 with a sample standard deviation of 0.395. What is the 99 percent confidence interval for the average EPS?

A market research firm surveys 500 adults and finds 421 own a smartphone. This gives a sample proportion of 0.842. What is q' for this sample?

In the formula for calculating sample size for a mean, n = (Z_alpha^2 * sigma^2) / e^2, what does 'e' represent?

A 95 percent confidence interval for the true mean number of colors on national flags is (2.93, 3.59). What is the most accurate interpretation of this interval?

To achieve a narrower confidence interval without changing the confidence level, what action should be taken?

For a confidence interval for a proportion, what is the point estimate for p, the true population proportion?

If you calculate a 90 percent confidence interval and a 95 percent confidence interval from the same data, which statement will be true?

What is the primary trade-off when choosing a confidence level for an interval estimate?