Course Extra for Part II. Quizzes  Any questions from the quizzes?

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Presentation transcript:

Course Extra for Part II

Quizzes  Any questions from the quizzes?

Study Guide  Any questions from the study guide?

Formulas Given What does a z-score actually mean? What is its unit of measurement?

Given

Understanding Confidence Intervals You take a random sample of 35 EMU students and record the time that it takes each of them to run a mile. A 95% confidence interval for the population mean is calculated to be (7:54, 8:43). Based on this interval, what could you say about the claim that the actual mean for all EMU students is 8:30? - We can’t make any statements about the claim without the p-value. - We have evidence that the mean for all students is 8:30, because it’s inside the interval. - We have convincing evidence that the mean is not 8:30, because it’s near the edge of the interval. - We don’t have evidence that the mean differs from 8:30, because 8:30 is inside the interval.

Do hints help on a cryptogram?  Students are randomly assigned into either the treatment (i.e., given hints) or no treatment (i.e., no hints) group and are then given a cryptogram to decipher. The time (in seconds) is recorded when the student solves the puzzle, with a maximum of 480 seconds.cryptogram  Does having the hints significantly lower the time required to solve the puzzle?

Cryptogram Results HintsNo Hints x bar s st error % Lower % Upper

Cryptogram Results

Statistical Results (we’ll interpret these in Chapter 18) t-Test: Two-Sample Assuming Unequal Variances Variable 1Variable 2 Mean Variance Observations15 Hypothesized Mean Difference0 df17 t Stat P(T<=t) one-tail t Critical one-tail P(T<=t) two-tail t Critical two-tail

Conclusions for Cryptogram Experiment  What would our decision be regarding the null?  What does this mean in common English?  What error could we have made?  What’s the chance that we made that error?

Additional Review  What does the Central Limit Theorem tell us?  Give an example of a research question that probably cannot be addressed with an experiment.  Random sampling vs. random assignment  What does the 95% mean in a 95% confidence interval?  How do you calculate a confidence interval?  How do you calculate a p-value?  Could you calculate a “confidence interval” around the population mean?