1. We say that a point estimator isunbiasedif (choose one):

its sampling distribution is centered exactly at the parameter it estimates.

the standard deviation of its sampling distribution decreases as the sample size increases.

its sampling distribution is normal.

its value is always equal to the parameter it estimates.

The next four questions refer to the following information:

A study was conducted in order to estimate , the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 81 U.S. adults gives a mean weekly computer usage time of 8.5 hours and that from prior studies, the population standard deviation is assumed to be = 3.6 hours.

2. Based on this information, what would be the point estimate for ?

81

8.5

3.6

None of the above.

3. We are 95% confident that the mean number of weekly hours that U.S. adults use computers at home is:

between 8.1 and 8.9.

between 7.8 and 9.2.

between 7.7 and 9.3.

between 7.5 and 9.5.

between 7.3 and 9.7.

4. Which of the following will provide a more informative (i.e., narrower) confidence interval than the one in problem 3?

Using a sample of size 400 (instead of 81).

Using a sample of size 36 (instead of 81).

Using a different sample of size 81.

Using a 90% level of confidence (instead of 95%).

Using a 99% level of confidence (instead of 95%).

Both using a sample of size 400 (instead of 81) and using a 90% level of confidence (instead of 95%)are correct.

Both using a sample of size 400 (instead of 81)sing a 99% level of confidence (instead of 95%)are correct.

5. How large a sample of U.S. adults is needed in order to estimate with a 95% confidence interval oflength1.2 hours?

6

12

20

36

144

These next two questions refer to the following information:

A researcher would like to estimate p, the proportion of U.S. adults who support recognizing civil unions between gay or lesbian couples.

6. If the researcher would like to be 95% sure that the obtained sample proportion would be within 1.5% of p (the proportion in the entire population of U.S. adults), what sample size should be used?

17,778

4,445

1,112

67

45

7. Due to a limited budget, the researcher obtained opinions from a random sample of only 2,222 U.S. adults. With this sample size, the researcher can be 95% confident that the obtained sample proportion will differ from the true proportion (p) by no more than (answers are rounded):

.04%

.75%

2.1%

3%

There is no way to figure this out without knowing the actual sample proportion that was obtained.