Inferences for Means

What do we use to ESTIMATE unknown parameters?

• Hypothesis Test

• Confidence Interval

• Trig Identity

• Guess and check

You have an SRS of 23 observations from large population. The distribution of sample values is roughly symmetric with no outliers. What critical value would you use to obtain a 98% confidence interval for the mean of the population?

• 2.177

• 2.183

• 2.326

• 2.500

• 2.508

A quality control inspector will measure the salt content (in milligrams) in a random sample of bags of potato chips from an hour of production. Which of the following would result in the smallest margin of error in estimating the mean salt content σ ?

• 90% confidence; n = 25 

• 90% confidence; n = 50 

• 95% confidence; n =25 

• 95% confidence; n =50 

• n=100 at any confidence level 

How can you reduce both Type I and Type II errors?

• it can't be reduced
• redo the tests
• increase the sample size
• tamper with the data

What interval should be used?

• 2 Sample t interval for means

• Paired procedures: one sample t interval

• Paired procedures: one sample t test

• 1 proportion z interval

What test should be used?

• 2 proportion z test

• 1 proportion z test

• 2 sample t test for means

• 1 sample t test for mean

What test should be performed?

• 2 sample t test for difference in means

• 1 sample t test for mean difference (paired t test)

• 2 proportion z test

What test should be used?

• 2 Sample t test for difference in means

• 2 proportion z test

• Paired t test

• 1 sample z test

Mrs. Trahan claims that her students' average score on the AP exam is 3.9.  A random sample of 50 of her students' scores produce a mean score of 3.1 with a standard deviation of 1.5.  Does this sample show evidence that Mrs. Trahan is overstating her average score?

• With a test statistic of -3.8 which is unlikely, it seems that Mrs. Trahan may be overstating her average AP score.
• With a test statistic of -4.7 which is unlikely, it seems that Mrs. Trahan may be overstating her average AP score.
• With a test statistic of -0.53 which is not unusual and this sample does not show evidence that Mrs. Trahan is overstating her average AP score.

A random sample of 25 Ohio students had a mean ACT score of 21 with a standard deviation of 1.2.  Which of the following is the 95% confidence interval for the true average ACT score for Ohio students?

• (20.53, 21.47)
• (18.648, 23.352)
• (20.505, 21.495)