Quiz 3

The data set is from a case-control study of smoking and Alzheimer’s disease. The data set has two variables of main interest:

• smoking a factor with four levels “None”, “<10”, “10-20”, and “>20” (cigarettes per day)
• disease a factor with three levels “Alzheimer”, “Other dementias”, and “Other diagnoses”.

Q1 Describe the largest group that has other dementias. Discuss it by number of cigarettes per day.

The largest group is the none smokers who smoke 0 cigarettes per day.

Q2 Describe one group that has more cases than expected given independence (by chance). Discuss it by number of cigarettes per day.

Other dementias, greater than 20 cigarettes per day.

Q3 Does smoking seem to matter in determining other dementias? Discuss your reason using the masaic chart above.

Smoking doesn’t seem to matter in determining other dementias because there is a lot of grey areas on the mosaic plot. There is one area where smoking more than 20 packs a day showed a correlation but the correlation is too small compared to the other grey areas.

Q4 Create correlation plot for RailTrail.

Hint: The RailTrail data set is from the mosaicData package.

Q5 List all four variables that have negative correlation with the number of trail users (volume).

fall -.25, spring -.04, cloudcover -.37, precip -.23 all have negative correlation with the number of trail users (volume).

Q6 What season seems to be least popular for trail users?

Fall is the least popular season because it has a strong negative correlation.

Q7 The correlation coefficient between hightemp and cloudcover is quite small. Would you be sure that the two variables are not related at all?

Hint: One word answer (e.g., yes or no) is NOT enough. Explain why.

The hightemp and cloudcover is quite small in fact, but the color of the square where they meet is white which suggests that they have no correlation at all.

Q7.a Continued from Q7. Create scatter plot. After examing the scatter plot, would you conclude that the two variables are not related at all?

Hint: Discuss your reason by explaining your scatter plot.

Hightemp and cloudcover are not related at all when looking at the scatterplot because almost all of the points are not touching and they are completely spread all over the scatterplot and the further apart the points are on a scatterplot the more unrelated they are.

Q8 Hide the messages, the code and its results on the webpage.

Hint: Use message, echo and results in the chunk options. Refer to the RMarkdown Reference Guide.

Q9 Display the title and your name correctly at the top of the webpage.

Q10 Use the correct slug.