Matched Pairs Designs (Ch. 7) Stat 217 – Day 26 Matched Pairs Designs (Ch. 7)

Last Time Be able to anticipate the strength of evidence against the null hypothesis based on characteristics of the data Sample sizes Observed difference Within group variability Know how these factors impact confidence interval calculations

Recap – Comparing Two Groups Ch. 5: Comparing Two Proportions Ch. 6: Comparing Two Means In both cases, had “independent samples” Separate samples from two populations (e.g., males and females) Randomized experiment (e.g., yawn seen and no yawn seed) Hypothetical but separate groups (Kristen Gilbert)

Do husbands tend to be older than wives? Descriptive Statistics Mean = 35.71 years SD = 14.56 years Mean = 33.83 years SD = 13.56 years

Can you swim as fast in syrup?

Matched Pairs Designs Control for “subject to subject” variability Some couples are younger, some older Some people run faster than others Some products cost more than others Instead of comparing apples to oranges, compare treatments within each obs. unit Expect the variability in the differences to be much smaller than the variability in the response Love to reduce variability! Easier to detect difference in the treatments

Paired data How create paired data? Why use paired data? Repeated measurements Before/after Everyone both treatments Two prices on same products Matching Match people of similar strength Why use paired data? How analyze paired data?

Data Collection Flip a coin Heads => Chocolate chip Tails => other chip Place the chip on your tongue and hold to the roof of your mouth Record the elapsed time once the chip has completely melted on its own Record on the form

Data Collection Will this study allow me to compare the difference in average melting time between peanut butter and chocolate chips? What are some reasons I may not find a statistically significant difference when I analyze the data? Anything I can do about that?

Data Collection Now take the other chip, same exact instructions as before Place the chip on your tongue and hold to the roof of your mouth Record the elapsed time once the chip has completely melted on its own Record on the form

To Do Finish Lab 5 Read through Section 7.2 Lab 6 pre-lab