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

2. 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

3. 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)

4. Do husbands tend to be older than wives?
Descriptive Statistics
Mean = years
SD = years
Mean = years
SD = years

6. Can you swim as fast in syrup?

9. 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

10. 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?

11. 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

12. 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?

13. 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

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