1. Statistics 400 - Lecture 15

2. zToday: 10.1-10.3 zAssign #5: 8.62, 8.70, 8.78, and yIn recent years, there has been growing concern about the health effects of video display terminals (VDTs). It is known that the miscarriage rate of a pregnancy under normal conditions is about 20%. In a survey of 15 part-time female employees who used VDTs at least 20 hours per week, there were 5 reported miscarriages. At the 1% significance level, is there evidence that exposure to VDTs is increasing the miscarriage rate? zDue next Thursday

3. Example: zAn insurance company want to know if the average speed at which men drive is greater than that of women drivers zThe company took a random sample of 22 cars driven by men on a highway and recorded the average speed of each driver zThe company took another random sample of 14 cars driven by women on the same highway and recorded the average speed of each driver zHow might you go about testing the hypothesis?

4. Inferences about Two Population Means zSituation: yHave 2 independent random samples yEach sample comes from a normal population yThe population standard deviations are equal yWant to test test a hypothesis about the population means

5. Example (continued): zThe hypothesis we wish to test is:

6. zTest Statistic: zWhere zWhen H 0 is true, t has a t-distribution with (n 1 +n 2 - 2) degrees of freedom

7. Computing a P-Value zP-Value depends on the alternative

8. Putting it all together zExample: zInsurance company wants to know if average speed at which men drive is greater than women drivers zCompany took a random sample of 22 cars driven by men on a highway and recorded the average speed of each driver zThey took another random sample of 14 cars driven by women on the same highway and recorded the average speed of each driver

9. zData:

10. Sample Statistics

14. zHypothesis: zTest Statistic: zP-Value:

15. Example: Gender Differences in Metered-Dose Inhaler-Spacer (MDI) Device Technique (Pharmacotherapy, 2000) zAsthma is a disease of chronic airway inflamation zA typical treatment for asthma is using inhaled formulations (e.g., corticosteroids) zProper usage consists of shaking the inhaler, slowly depressing the cannister and simultaneously inhaling over 3-5 seconds and then holding in the breath for 10 seconds zStudy in 1990’s indicated gender differences in the usage of the MDI

16. Example: Gender Differences in Metered-Dose Inhaler-Spacer (MDI) Device Technique (Pharmacotherapy, 2000) zStudy performed to determine whether gender affects the correct use of MDI device z83 3 rd year Doctor of Pharmacy students (31 men; 52 women) were given a placeobo MSI and 20 minutes training on the device zOne week later, the students returned and were tested on their ability to use the device…each student was assigned a score in usage by the tester zMean score for males was 8.68 and mean score for women was 8.65 with sample standard deviations of 3.62 and 4.00 respectively zWhat do these data indicate?