**Practice Problems: Confidence Intervals**

A sample of Alzheimer's patients are tested to assess the amount of time in stage IV sleep. It has been hypothesized that individuals sufferering from Alzheimer's Disease may spend less time per night in the deeper stages of sleep. Number of minutes spent is Stage IV sleep is recorded for sixty-one patients. The sample produced a mean of 48 minutes (S=14 minutes) of stage IV sleep over a 24 hour period of time. Compute a 95 percent confidence interval for this data. What does this information tell you about a particular individual's (an Alzheimer's patient) stage IV sleep?

Answer

A university wants to know more about the knowledge of students regarding international events. The are concerned that their students are uninformed in regards to new from other countries. A standardized test is used to assess students knowledge of world events (national reported mean=65, S=5). A sample of 30 students are tested (sample mean=58, Standard Error=3.2). Compute a 99 percent confidence interval based on this sample's data. How do these students compare to the national sample?

Answer

A sample of students from an introductory psychology class were polled regarding the number of hours they spent studying for the last exam. All students anonymously submitted the number of hours on a 3 by 5 card. There were 24 individuals in the one section of the course polled. The data was used to make inferences regarding the other students taking the course. There data are below:

4.5 | 22 | 7 | 14.5 | 9 | 9 | 3.5 | 8 | 11 | 7.5 | 18 | 20 |

7.5 | 9 | 10.5 | 15 | 19 | 2.5 | 5 | 9 | 8.5 | 14 | 20 | 8 |

Compute a 95 percent confidence interval. What does this tell us?

Answer

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