Independent Independent Samples: Samples:

Comparing Comparing ProportionsProportionsLecture 42Lecture 42

Section 11.5Section 11.5

Fri, Apr 8, 2005Fri, Apr 8, 2005

Confidence IntervalsConfidence Intervals

A confidence interval for A confidence interval for pp11 – – pp22 is of is of the formthe form

21 ˆˆ21 ˆˆ ppzpp

oror

1

22

1

1121

ˆ1ˆˆ1ˆˆˆ

n

pp

n

ppzpp

Confidence IntervalsConfidence Intervals

Since we are trying to estimate the Since we are trying to estimate the difference between difference between pp11 and and pp22, it , it

would not make sense to use the would not make sense to use the pooled estimate ofpooled estimate of..

ExampleExample

Re-do Example 11.8, p. 669, as a Re-do Example 11.8, p. 669, as a confidence interval problem.confidence interval problem.

Confidence Intervals on Confidence Intervals on the TI-83the TI-83

Press STAT.Press STAT. Select 2-PropZInt.Select 2-PropZInt.

A window appears.A window appears.

Enter Enter xx11..

Enter Enter nn11..

Enter Enter xx22..

Enter Enter nn22..

Confidence Intervals on Confidence Intervals on the TI-83the TI-83

Enter the confidence level.Enter the confidence level. Select Calculate.Select Calculate. Press ENTER.Press ENTER.

Confidence Intervals on Confidence Intervals on the TI-83the TI-83

A window appears with the following A window appears with the following information.information. The confidence interval for The confidence interval for pp11 – – pp22..

The value of The value of pp11^̂..

The value of The value of pp22^̂..

nn11..

nn22..

ExampleExample

Re-do Example 11.8, p. 669, using Re-do Example 11.8, p. 669, using the TI-83.the TI-83.

Let’s Do It!Let’s Do It!

Let’s do it! 11.7, p. 671 – HMOs on Let’s do it! 11.7, p. 671 – HMOs on the Rise.the Rise.