Lesson 5.pdf

Lesson 5.pdf - Lesson 5 Comparing Two Means Using...

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Lesson 5: Comparing Two Means Using Confidence Intervals In previous lesson we covered the calculation and interpretation of confidence intervals for a single population mean ࠵? . This chapter covers the comparing two population means. Standard way to compare two population means ࠵? ! and ࠵? ! is by estimating their difference, ࠵? ! ࠵? ! . Recall the confidence interval for ࠵? Using the same analogy we can guess the form of the confidence interval for ࠵? ! ࠵? ! . Formula for the confidence interval for ࠵? ࠵? ࠵? ࠵? is: Here, d.f of t*=smallest of (n 1 -1) and (n 2 -1)

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Example 1 : Recall the migraine medication problem we did before. I gave you the true mean relief time for the standard drug and asked whether new drug is better or worse than the standard drug. Let’s say that we don’t know the true mean relief time for the standard drug but the researcher has collected data from two groups of migraine patients. Group 1: 25 patients on new drug. They have mean relief time of 7.5 minutes with standard deviation of 2.1 minutes. Group 2: 30 patients on standard drug. They have mean relief time of 14.3 minutes with standard deviation 3.2 minutes.
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