This CRAZY thing called“INFERENCE” Used to try and gain some knowledge about an unknown population parameter (usually µ or p) If we don’t know the value of a parameter, we might try to… > calculate a range of believable values for it (this is a Confidence Interval) or > test it against a specific value that we think may or may not be true (this is a Hypothesis Test).

Section 12-2: Inference for The Difference Between Two Proportions With a confidence interval you are estimating the difference in two population proportions. When you perform a hypothesis test, you are testing if two population proportions are equal (that is, if the difference between them is zero).

So we want to estimate the value of this quantity with a CI: Or maybe instead we want to compare the two proportions with an HT:

Section 12-2: Hypothesis Test for Comparing the Values of Two Proportions (pg 708) (equivalently: ) Note: NEVER EVER calculate this by hand! Note #2: When using the calculator, make sure that x1 and x2 are whole numbers.

Chapters 10&12 vocabulary -- our previous unit Reminder: (7) All Hypothesis Tests are set up the same way, no matter what chapter, distribution, or parameter symbol we are using!

HCCC Chapter 10 Vocabulary (11) Again, how can we remember all of the steps involved in performing a Hypothesis Test? HCCC H = write your two Hypotheses C = check the Conditions C = perform the Calculations C = write a Conclusion

Packet page 8 (left side) (1997 #3) A candidate made some “unfortunate remarks”; polls were taken both before and after he did this. Is there good evidence That his remarks caused An overall decrease in Voter support?

Here’s one for you to try! Packet page 9, 2009B #3 What worked better for heart attack victims – CPR or a cardiopump?

And now………A FEW REMINDERS ABOUT CI’S The assumptions, names, and formulas DO change for the different types of problems. The structure and interpretation of the confidence intervals DO NOT change. The set-up for ALL Confidence Intervals is Statistic + critical value ∙ standard deviation/error of statistic

For Example: Social media researchers are curious as to whether texting rates differ between teenage boys vs girls. Specifically, they are interested in the difference between the proportion of teenage boys who text at least once an hour and the proportion of teenage girls who text at least once an hour.

So they want to estimate the value of this quantity with a Confidence “Social media researchers are curious as to whether texting rates differ between teenage boys versus girls. Specifically, they are interested in the difference between the proportion of teenage boys who text at least once an hour and the proportion of teenage girls who text once an hour.” So they want to estimate the value of this quantity with a Confidence Interval: That is, they want to create a set of believable values for this difference.

CCC Chapter 10 Vocabulary Once again, how can we remember all of the steps involved in constructing a Confidence Interval? CCC C = check the Conditions C = perform the Calculations C = write a Conclusion

Confidence Interval for the difference between two proportions (pg 704) This formula is way too tough to do by hand!

Practice Time! Packet page 10, 2006B #2 Are the night shift factory workers too sleepy to do good work? See the “Conditions” summary on the “Hypothesis Testing Study Guide”!