Interval Estimation

Question 1

The absolute value of the difference between the point estimate and the population parameter it estimates is

Answer 1

the sampling error

Question 2

A population has a standard deviation of 50. A random sample of 100 items from this population is selected. The sample mean is determined to be 600. At 95% confidence, the margin of error is

Answer 2

9.8

Question 3

For the interval estimation of  when  is known and the sample is large, the proper distribution to use is

Answer 3

the normal distribution

Question 4

The value added and subtracted from a point estimate in order to develop an interval estimate of the population parameter is known as the

Answer 4

margin of error

Question 5

In order to use the normal distribution for interval estimation of ‘mean’ when ‘sigma’ is known and the sample is very small, the population

Answer 5

must have a normal distribution

Question 6

The z value for a 97.8% confidence interval estimation is

Answer 6

2.29

Question 7

After computing a confidence interval, the user believes the results are meaningless because the width
of the interval is too large. Which one of the following is the best recommendation?

Answer 7

Increase the sample size.

Question 8

In general, higher confidence levels provide

Answer 8

wider confidence intervals

Question 9

A sample of 225 elements from a population with a standard deviation of 75 is selected. The sample mean is 180. The 95% confidence interval for ‘mean’ is

Answer 9

170.2 to 189.8

Question 10

A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 4.8. The 95.44% confidence interval for the population mean is

Answer 10

19.200 to 20.800

Question 11

When s is used to estimate sigma, the margin of error is computed by using

Answer 11

t distribution

Question 12

As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution

Answer 12

becomes smaller

Question 13

In interval estimation, the t distribution is applicable only when

Answer 13

the sample standard deviation is used to estimate the population standard deviation

Question 14

From a population that is not normally distributed and whose standard deviation is not known, a sample of 6 items is selected to develop an interval estimate for the mean of the population (‘mean’).

Answer 14

The sample size must be increased.

Question 15

The t value for a 95% confidence interval estimation with 24 degrees of freedom is

Answer 15

2.064

Question 16

A sample of 20 items from a population with an unknown  is selected in order to develop an interval estimate of ‘mean’. Which of the following is not necessary?

Answer 16

The sample must have a normal distribution.

Question 17

When constructing a confidence interval for the population mean and the standard deviation of the sample is used, the degrees of freedom for the t distribution equals

Answer 17

n-1

Question 18

The following random sample from a population whose values were normally distributed was collected.
10 12 18 16
The 80% confidence interval for ‘mean’ is

Answer 18

11.009 to 16.991

Question 19

As the sample size increases, the margin of error

Answer 19

decreases

Question 20

The sample size needed to provide a margin of error of 2 or less with a .95 probability when the population standard deviation equals 11 is

Answer 20

117

Question 21

For which of the following values of P is the value of P(1 - P) maximized?

Answer 21

P = 0.50

Question 22

Using an alpha = 0.04 a confidence interval for a population proportion is determined to be 0.65 to 0.75. If the level of significance is decreased, the interval for the population proportion

Answer 22

becomes wider

Question 23

In a random sample of 144 observations, p = 0.6. The 95% confidence interval for P is

Answer 23

0.52 to 0.68

Question 24

A random sample of 1000 people was taken. Four hundred fifty of the people in the sample favored Candidate A. The 95% confidence interval for the true proportion of people who favors Candidate A is

Answer 24

0.419 to 0.481

Question 25

We are interested in conducting a study in order to determine what percentage of voters of a state would vote for the incumbent governor. What is the minimum size sample needed to estimate the population proportion with a margin of error of 0.05 or less at 95% confidence?

Answer 25

385