STATS CH12

22 Pollsters tend to use larger samples than researchers for a number of reasons including the notion that, in surveys, samples a) can't ever be too large. b) often contain observations that are relatively easy to obtain. c) both a and b d) neither a nor b

c) both a and b

4 An investigator claims, with 95 percent confidence, that the interval between 10 and 16 miles includes the mean one-way commute distance for all California commuters. To have 95 percent confidence signifies that a) the unknown population mean is definitely between 10 and 16 miles. b) the unknown population mean is between 10 and 16 miles with probability .95. c) if these intervals were constructed for a long series of samples, approximately 95 percent would include the unknown mean commute distance for all Californians. d) if sample means were obtained for a long series of samples, approximately 95 percent of all sample means would be between 10 and 16 miles.

c) if these intervals were constructed for a long series of samples, approximately 95 percent would include the unknown mean commute distance for all Californians.

8 Although we never really know whether a particular 95 percent confidence interval is true or false, we can be "reasonably confident" that a) a second confidence interval would describe exactly the same range of values as the first confidence interval. b) a long series of confidence intervals would include the unknown population mean. c) the one observed confidence interval includes the unknown population mean. d) the one observed confidence interval contains the observed sample mean.

c) the one observed confidence interval includes the unknown population mean.

10 Any shift to a higher confidence level produces a a) narrower, less precise confidence interval. b) narrower, more precise confidence interval. c) wider, less precise confidence interval. d) wider, more precise confidence interval.

c) wider, less precise confidence interval.

3 Confidence intervals for the population mean specify a) the value of the population mean. b) the value of the population mean with a known degree of confidence. c) a range of values that includes the population mean. d) a range of values that includes the population mean with a known degree of confidence.

d) a range of values that includes the population mean with a known degree of confidence.

9 The level of confidence indicates the percent of time that a) a particular confidence interval is true. b) a particular confidence interval contains the unknown population mean. c) a series of confidence intervals are centered about the unknown population mean. d) a series of confidence intervals include the unknown population mean.

d) a series of confidence intervals include the unknown population mean.

17 Consider the use of a a) hypothesis test whenever a confidence interval has been constructed. b) hypothesis test whenever you suspect the null hypothesis to be true. c) confidence interval whenever the null hypothesis has been retained. d) confidence interval whenever the null hypothesis has been rejected.

d) confidence interval whenever the null hypothesis has been rejected.

5 A false 95 percent confidence interval would be produced if, in fact, the one observed sample mean a) coincides with the unknown population mean. b) deviates onehalf of a standard error unit above the unknown population mean. c) deviates one and onehalf standard error units below the unknown population mean. d) deviates three standard error units above the unknown population mean.

d) deviates three standard error units above the unknown population mean.

15 To generate a confidence interval that possesses a desired width, yet complies with a desired level of confidence, refer to formulas (in other books) for the selection of an appropriate a) confidence interval. b) interval width. c) level of confidence. d) sample size.

d) sample size.

23 Prior to attending college, randomly selected college-bound students participate in a summer workshop on the development of good study habits. Subsequently, at the end of their first year in college, they showed a dramatic increase in grade point averages, relative to the national average of 2.75, as revealed by a 95 percent confidence interval of 2.90 to 3.30. This confidence interval signifies that a) every student who participated in the summer workshop had a GPA between 2.90 and 3.30. b) about 95 percent of all students who participated in the summer workshop had GPAs between 2.90 and 3.30. c) the true population mean (for all students who could conceivably take the summer workshop) is between 2.90 and 3.30. d) we can be reasonably confident that the true population mean (for all students who could conceivably take the summer workshop) is between 2.90 and 3.30.

d) we can be reasonably confident that the true population mean (for all students who could conceivably take the summer workshop) is between 2.90 and 3.30.

14 As sample size grows larger, a confidence interval approaches a a) population survey. b) point estimate. c) standard error. d) population range.

b) point estimate.

11 Although many different confidence levels have been used, the two most prevalent levels are a) 90 and 95 percent. b) 90 and 99 percent. c) 95 and 99 percent. d) 99 and 99.9 percent.

c) 95 and 99 percent.

12 Generally speaking, a larger level of confidence should be reserved for those situations where a) a true interval must be described precisely. b) a true interval must be described with convenient numbers. c) a false interval has serious consequences. d) a false interval has relatively unimportant consequences.

c) a false interval has serious consequences.

6 To understand why confidence intervals work, it's important to view the observed sample mean as originating from a a) single random sample that reflects the unknown population mean. b) sampling distribution that is centered about the unknown population mean. c) population that is centered about the unknown population mean. d) confidence interval that will be true 95 percent of the time.

b) sampling distribution that is centered about the unknown population mean.

16 Confidence intervals tend to be more informative than hypothesis tests because confidence intervals indicate a) whether or not an effect is present. b) the possible size of the effect. c) the probability that there is an effect. d) the percent of times that the effect is present.

b) the possible size of the effect.

24 Specify which one of the following 95 percent confidence intervals would be most preferable, given that you wish to demonstrate that a summer workshop increases GPAs. a) 2.70 to 3.30 b) 2.50 to 3.50 c) 2.90 to 3.40 d) 2.80 to 3.40

c) 2.90 to 3.40

20 A pollster reports, with 95 percent confidence, that between 55 and 61 percent of all Americans favor mandatory drug testings for employees in positions of public trust (bus drivers, airline pilots, etc). The point estimate for the unknown population proportion (who favor mandatory drug testing) equals a) 55 percent. b) 58 percent. c) 61 percent. d) some unknown percent.

b) 58 percent.

1 Given a sample mean of 130 and a sample standard deviation of 20, a point estimate of the unknown population mean would equal a) 130 b) 130/20 c) 130 plus or minus 20 d) approximately 90 to 170

a) 130

19 A pollster reports, with 95 percent confidence, that between 55 and 61 percent of all Americans favor mandatory drug testings for employees in positions of public trust (bus drivers, airline pilots, etc). The margin of error in this survey equals a) 3 percent. b) 6 percent. c) 55 percent. d) some unknown percent.

a) 3 percent.

21 A pollster reports, with 95 percent confidence, that between 55 and 61 percent of all Americans favor mandatory drug testings for employees in positions of public trust (bus drivers, airline pilots, etc). The boundaries of this confidence interval (55 to 61 percent) suggest that a) a majority of Americans probably favor mandatory drug testing. b) a majority of Americans definitely favor mandatory drug testing. c) it is impossible to know whether a majority of Americans favor mandatory drug testing. d) all of the above are true, depending on your perspective.

a) a majority of Americans probably favor mandatory drug testing.

7 In practice, a single 95 percent confidence interval is either true or false because it either a) includes or fails to include the unknown population mean. b) aligns itself or fails to align itself symmetrically about the unknown population mean. c) originates or fails to originate from the true sampling distribution. d) originates or fails to originate from the true population.

a) includes or fails to include the unknown population mean.

13 The larger the sample size, a) the smaller the standard error and the narrower the confidence interval. b) the smaller the standard error and the wider the confidence interval. c) the larger the standard error and the narrower the confidence interval. d) the larger the standard error and the wider the confidence interval.

a) the smaller the standard error and the narrower the confidence interval.

18 Often encountered in national polls are sample sizes of about a) 10,000 b) 1,500 c) 500 d) 100

b) 1,500

2 Point estimates suffer from a basic deficiency they tend to be a) biased. b) inaccurate. c) difficult to interpret. d) imprecise.

b) inaccurate.