Quiz3

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”.

library(tidyverse)

## ── Attaching packages ────────────────────────────── tidyverse 1.3.0 ──

## ✓ ggplot2 3.3.0     ✓ purrr   0.3.3
## ✓ tibble  2.1.3     ✓ dplyr   0.8.5
## ✓ tidyr   1.0.2     ✓ stringr 1.4.0
## ✓ readr   1.3.1     ✓ forcats 0.5.0

## ── Conflicts ───────────────────────────────── tidyverse_conflicts() ──
## x dplyr::filter() masks stats::filter()
## x dplyr::lag()    masks stats::lag()

# Import data
data("alzheimer", package = "coin")

# create a table
tbl <- xtabs(~disease + smoking, alzheimer)
ftable(tbl)

##                 smoking None <10 10-20 >20
## disease                                   
## Alzheimer                126  15    30  27
## Other dementias           79   8    33  44
## Other diagnoses          104   5    47  20

# create a mosaic plot from the table
library(vcd)

## Loading required package: grid

mosaic(tbl, 
       shade = TRUE,
       legend = TRUE,
       labeling_args = list(set_varnames = c(disease = "")),
       set_labels = list(disease = c("Alzheimer", "Other\ndementias", "Other\ndiagnoses")))

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

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

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).

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

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.

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.

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.