invest_3ed.pdf

# M now press shuffle four more times does the number

• 429
• 60% (5) 3 out of 5 people found this document helpful

This preview shows pages 214–217. Sign up to view the full content.

(m) Now press Shuffle four more times. Does the number of successes vary among the repetitions? (n) Enter 995 for the Number of shuffles . This produces a total of 1000 repetitions of the simulated random assignment process under the null hypothesis (the “null distribution”) . What is the value of the mean of this null distribution? Explain why this center makes intuitive sense. (o) Now we want to compare the observed result from the research study to these “could have been” results under the null hypothesis. x How many improvers were there in the Dolphin therapy group in the actual study? x Based on the resulting dotplot, does it seem like the actual experimental results would be surprising to arise solely from the random assignment process under the null model that dolphin therapy is not effective? Explain. (p) In the Count Samples box, enter the observed statistic from the actual study and press Count to have the applet count the number of repetitions with 10 or more successes in the Dolphin group. In what proportion of your 1000 simulated random assignments were the results as (or more) extreme as the actual study? (q) We said above that it would be equivalent to look at the difference in the conditional proportions. Use the Statistic pull-down menu (on far left side) to select Difference in proportions. How does the null distribution (including the mean) change? Does this make sense? How does the p-value change?

This preview has intentionally blurred sections. Sign up to view the full version.

Chance/Rossman, 2015 ISCAM III Investigation 3.6 214 (r) Interpret the p-value you found [ Hint : Same reasoning as before, but now also focus on the source of randomness that was modelled in the simulation.] (s) Is this empirical p-value small enough to convince you that the experimental data that the researchers obtained provide strong evidence that dolphin therapy is effective (i.e., that the null model is not correct)? (t) Is it reasonable to attribute the observed difference in success proportions to the dolphin therapy alone? Explain. (u) To what population is it reasonable to generalize these results? Justify your answer. Discussion : This procedure of randomly reassigning the response variable outcomes to the explanatory variable groups is often called a “randomization test.” The goal is to assess the chance variability from the random assignment process (as opposed to random sampling), though it is sometimes used to approximate the random chance arising from random sampling as well. Use of this procedure models the two-way table with fixed row and column totals (e.g., people were going to improve or not regardless of which treatment they received).
Chance/Rossman, 2015 ISCAM III Investigation 3.6 215 Study Conclusions Due to the small p-value (0.01 < p-value < 0.05) from our “randomization test , we have moderately strong evidence that “luck of the draw” of the random assignment process alone is not a reasonable explanation for the higher proportion of subjects who substantially improved in the dolphin therapy group compared to the control group. Thus the researchers have moderate evidence that subjects aged 18

This preview has intentionally blurred sections. Sign up to view the full version.

This is the end of the preview. Sign up to access the rest of the document.
• Spring '14
• -STAFF

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern