Comparing Two Proportions Section 13 2 Confidence Intervals

Comparing Two Proportions Section 13. 2

Confidence Intervals Step 1: State what you are looking for…We are looking for the difference in proportions of… Step 2: Conditions *SRS/Random Assignment *Normality: *Independence: Samples are independent of each other

�Step 3: Calculations �Step 4: Conclusions We are ___% confident that the difference in the proportions of…is between…

Example: Data on page 807 Does prayer help in vitro fertilization? �Random assignment into 2 groups: treatment group, where people prayed for them, and a control �Treatment: 44/88 women got pregnant �Control: 21/81 women got pregnant

Example: Does random drug testing reduce illegal drug use? � 2 schools in Oregon: one had random testing and the other did not �Drug testing: 7/135 �No testing: 27/141

2 Proportion Significance Tests Section 13. 2

Step 1: where p 1=… and p 2=…

Step 2: • SRS/Random Assignment • Normality: all must be greater than 5 • Independence: samples are independent

Step 3: Sig Tests of H 0 : p 1 = p 2 use the combined sample proportion: P-value=

Step 4: Interpretation Reject/fail to reject If the proportions were equal, the probability that would obtain a difference of _____ is (p-value)%. We have evidence/ no evidence that…

Example: Seat Belt Use In New York City, police can stop a driver who is not belted. In Boston, police can cite a driver for not wearing a seat belt only if they have been stopped for something else. A random sample of female Hispanic drivers in the two cities shows: City Drivers Belted New York 220 183 Boston 117 68 Conduct a significance test to determine if there is a significant difference in the proportion of drivers wear seat belts in Boston rather than in New York.

Homework: pg. 813 #27 pg. 819 #29, 32