Statistics and Statistical Programming (Winter 2017)/Problem Set: Week 6

Programming Challenges

Let's re-evaluate some data from this paper:

Lagakos, S., & Mosteller, F. (1981). A case study of statistics in the regulatory process: the FD&C Red No. 40 experiments. Journal of the National Cancer Institute, 66(1), 197–212. [PDF]

PC0. Download the dataset by clicking through on the "Red Dye Number 40" link on this webpage. You'll find that the it's not in an ideal setup. It's an Excel file (XLS) with a series of columns labeled X1.. X4. The format is not exactly tabular.

PC1. Load the data into R. Now get to work on reshaping the dataset. I think a good format would be a data frame with two columns: group, time of death (i.e., lifespan).

PC2. Create summary statistics and visualizations for each group. Write code that allows you to generate a useful way to both (a) get a visual sense both for the shape of the data and its relationships and (b) the degree to which the assumptions for t-tests and ANOVA hold. What is the global mean of your dependent variable?

PC3. Do a t-test between mice with none RD40 and mice with any (i.e., at least a small amount). Next, run a t-test between the group with a high dosage and control group. How would you go about doing it using formula notation? Be ready to report, interpret, and discuss the results in substantive terms.

PC4. Estimate an ANOVA analysis using aov() to see if there is a difference between the groups. Be ready to report, interpret, and discuss the results in substantive terms.

Statistical Questions from OpenIntro §6

Q0. Any questions or clarifications from the OpenIntro text or lecture notes?

Q1. Exercise 6.12 on public opinion about cannabis legalization

Q2. Exercise 6.20 a continuation of 6.12

Q3. Exercise 6.38 on translating a problem in English into statistical tests

Q4. Exercise 6.50 another voter/public opinion question

Questions on the Empirical Paper

Let's just go back to the Buechley and Hill paper on LilyPad Arduino:

Q5. For Study 1, lets focus on the statistical test:

• (a) What is the unit of analysis? What is the dependent variable? The independent variable? What are groups being compared in the test? Is it a one-way or two-way design?
• (b) What is the null hypothesis being tested? What is the alternative hypothesis?
• (c) Summarize ore restate results in statistical terms. Explain what these results mean in substantive terms? How convincing do you find these results? What should we be taking away?
• (d) Why weren't we happy just leaving it where we did in week 2? Why bother with the statistical test?

Q6. Do the same as above but for Study 2.

Questions on Gelman and Loken

Q7. Be ready to summarize the main point of, and share some reflections on, the paper. There are no specific questions.