Homework 9

load(url("http://www.rossmanchance.com/iscam3/ISCAM.RData"))
library(dplyr)
library(ggplot2)
homework at: http://www.rossmanchance.com/iscam3/instructors.html

Chapter 3 HW 13

Pet Birds and Lung Cancer? Researchers investigated whether owning a pet bird might be associated with having lung cancer. They studied a sample of 239 lung cancer patients and a sample of 429 people who did not have lung cancer, chosen to have similar characteristics to those with lung cancer. They asked all subjects whether they owned a pet bird in adulthood.

  1. Identify the explanatory and response variables in this study.

  2. What kind of observational study is this: case-control, cohort, or cross-classification? Explain briefly.

The researchers found that 98 of the lung cancer patients owned a pet bird, and 101 of those without lung cancer owned a pet bird.

  1. Organize these data into a 2×2 table, with the explanatory variable in columns.

  2. Calculate the odds ratio of having lung cancer, comparing those who owned a pet bird to those who did not.

  3. Use the normal approximation to test whether these data provide strong evidence that the probability of lung cancer differs between those who owned a pet bird and those who did not. Report the hypotheses, test statistic and p-value, along with the test decision at the 0.05 significance level. Also verify that the technical conditions are satisfied, and summarize your conclusion from this test.

  4. Produce a 95% confidence interval for the odds ratio of having lung cancer between the two populations. Also interpret this interval.

  5. Summarize your conclusion from this study and your analysis. Be sure to address the issues of causation and generalizability as well as statistical significance.

Chapter 4 HW 3

2015 Wimbledon (cont.) Reconsider the 2015 Wimbledon tennis data again (http://www.rossmanchance.com/iscam3/data/Wimbledon2015.txt).
Use technology to analyze the men’s and women’s distributions of the sets, games, and time variables. For each of these three variables, produce graphical and numerical summaries to compare the distributions between the two sexes, and write a paragraph comparing and contrasting them.

Chapter 4 HW 4

2015 Wimbledon (cont.) Reconsider the 2015 Wimbledon tennis data yet again (http://www.rossmanchance.com/iscam3/data/Wimbledon2015.txt).

  1. Use technology to create three new variables:
    • Ratio of games to sets
    • Ratio of points to games
    • Ratio of time to points

Analyze these data to investigate whether men and women differ with regard to the distributions of these variables. For each of these three variables, produce graphical and numerical summaries to compare the distributions between the two sexes, and write a paragraph comparing and contrasting them.

  1. Use technology to create a new variable: winner points - loser points and examine the distribution of this point differential separately for males and females. Which sex tended to have smaller differentials? What does this imply? Which sex tended to have more variability in the differentials? What does this imply? How often did the winner score fewer points than the loser? Explain how this can happen in this context.

Chapter 4 HW 5

Feeling Motivated?

A psychology study investigated whether people display more creativity when they are thinking about intrinsic or extrinsic motivations. The subjects were 47 people with extensive experience with creative writing. They were randomly assigned to one of two groups: one group answered a survey about intrinsic motivations for writing (such as the pleasure of self-expression) and the other group answered a survey about extrinsic motivations (such as public recognition). Then all subjects were instructed to write a Haiku poem, and these poems were evaluated for creativity by a panel of judges. The researchers conjectured that subjects who were thinking about intrinsic motivations would display more creativity than subjects who were thinking about extrinsic motivations. The creativity scores from this study are below and also in the file creativity.txt (http://www.rossmanchance.com/iscam2/data/creativity.txt).

  1. Identify the explanatory and response variables. Also classify each as categorical or quantitative.

  2. Is this an observational study or a randomized experiment? Explain how you know.

  3. Examine the dotplots of the sample data produced by the Comparing Groups applet (http://www.rossmanchance.com/applets/AnovaShuffle.htm). Submit a screen capture of these graphs, and comment on what they reveal about the researchers’ conjecture.

  4. Report the mean of the creativity scores for each group. Do these summary values indicate that the intrinsically motivated group did indeed display more creativity than the intrinsically motivated group?

  5. Carry out a randomization test using technology to the data provide statistically significant evidence that the type of motivation causes affects creativity score in the conjectured direction. Submit a screen capture of the resulting dotplot, and answer four questions:
    1. Describe the null model that underlies this simulation analysis.
    2. Explain what variable is displayed in the dotplot.
    3. Describe what the dotplot reveals.
    4. Report the approximate p-value.

  6. Summarize your conclusion in the context of this study. Include an explanation of the reasoning process behind your conclusion. Be sure to address the issues of causation (i.e., is a cause-and-effect conclusion warranted?) and generalizability (i.e., how broadly can you legitimately generalize your conclusion?), as well as the issue of statistical significance.