---
title: "Chapter 2 - Summarizing Data"
author: ""
output:
pdf_document:
extra_dependencies: ["geometry", "multicol", "multirow"]
editor_options:
chunk_output_type: console
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
**Stats scores**. (2.33, p. 78) Below are the final exam scores of twenty introductory statistics students.
57, 66, 69, 71, 72, 73, 74, 77, 78, 78, 79, 79, 81, 81, 82, 83, 83, 88, 89, 94
Create a box plot of the distribution of these scores. The five number summary provided below may be useful.
\begin{center}
\renewcommand\arraystretch{1.5}
\begin{tabular}{ccccc}
Min & Q1 & Q2 (Median) & Q3 & Max \\
\hline
57 & 72.5 & 78.5 & 82.5 & 94 \\
\end{tabular}
\end{center}
```{r, echo = FALSE}
scores <- c(57, 66, 69, 71, 72, 73, 74, 77, 78, 78, 79, 79, 81, 81, 82, 83, 83, 88, 89, 94)
```
--------------------------------------------------------------------------------
\clearpage
**Mix-and-match**. (2.10, p. 57) Describe the distribution in the histograms below and match them to the box plots.
```{r, echo=FALSE, message=FALSE, warning=FALSE, fig.width=10, fig.height=3}
library(openintro)
set.seed(7365)
sym = rnorm(1000, mean = 60, sd = 3)
uni = runif(1000, min = 0, max = 100)
rs = rgamma(1000, shape = 3, rate = 2)
par(mar=c(4, 3.6, 0, 0), las = 1, mgp = c(2.7, 0.7, 0),
mfrow = c(1,6),
cex.lab = 1.5, cex.axis = 1.5)
histPlot(sym, xlab = "(a)", ylab = "", col = COL[1], axes = FALSE)
axis(1, seq(50,70,10))
histPlot(uni, xlab = "(b)", ylab = "", col = COL[1], axes = FALSE)
axis(1, seq(0,100,50))
histPlot(rs, xlab = "(c)", ylab = "", col = COL[1], axes = FALSE)
axis(1, seq(0,6,2))
boxPlot(rs, xlab = "(1)", ylab = "", col = COL[1,3])
boxPlot(sym, xlab = "(2)", ylab = "", col = COL[1,3])
boxPlot(uni, xlab = "(3)", ylab = "", col = COL[1,3])
```
--------------------------------------------------------------------------------
\clearpage
**Distributions and appropriate statistics, Part II**. (2.16, p. 59) For each of the following, state whether you expect the distribution to be symmetric, right skewed, or left skewed. Also specify whether the mean or median would best represent a typical observation in the data, and whether the variability of observations would be best represented using the standard deviation or IQR. Explain your reasoning.
(a) Housing prices in a country where 25% of the houses cost below $350,000, 50% of the houses cost below $450,000, 75% of the houses cost below $1,000,000 and there are a meaningful number of houses that cost more than $6,000,000.
(b) Housing prices in a country where 25% of the houses cost below $300,000, 50% of the houses cost below $600,000, 75% of the houses cost below $900,000 and very few houses that cost more than $1,200,000.
(c) Number of alcoholic drinks consumed by college students in a given week. Assume that most of these students donâ€™t drink since they are under 21 years old, and only a few drink excessively.
(d) Annual salaries of the employees at a Fortune 500 company where only a few high level
executives earn much higher salaries than the all other employees.
--------------------------------------------------------------------------------
\clearpage
**Heart transplants.** (2.26, p. 76) The Stanford University Heart Transplant Study was conducted to determine whether an experimental heart transplant program increased lifespan. Each patient entering the program was designated an official heart transplant candidate, meaning that he was gravely ill and would most likely benefit from a new heart. Some patients got a transplant and some did not. The variable *transplant* indicates which group the patients were in; patients in the treatment group got a transplant and those in the control group did not. Of the 34 patients in the control group, 30 died. Of the 69 people in the treatment group, 45 died. Another variable called *survived* was used to indicate whether or not the patient was alive at the end of the study.
```{r, echo=FALSE, message=FALSE, warning=FALSE, fig.show="hold", out.width="50%", fig.height=3}
library(openintro)
data(heartTr)
# mosaic plot -------------------------------------------------------
par(mar = c(0, 0, 0, 0), las = 1, mgp = c(2.7, 0.9, 0))
mosaicplot(transplant ~ survived, data = heartTr,
main = "", xlab = "", ylab = "", color = COL[1],
cex.axis = 1.5)
# box plot ----------------------------------------------------------
par(mar = c(2, 4.8, 0, 0), las = 1, mgp = c(3.5, 0.7, 0),
cex.lab = 1.5, cex.axis = 1.5)
boxPlot(heartTr$survtime, fact = heartTr$transplant,
ylab = "Survival Time (days)", col = COL[1,2])
```
(a) Based on the mosaic plot, is survival independent of whether or not the
patient got a transplant? Explain your reasoning.
(b) What do the box plots below suggest about the efficacy (effectiveness) of the heart transplant treatment.
(c) What proportion of patients in the treatment group and what proportion of
patients in the control group died?
(d) One approach for investigating whether or not the treatment is effective
is to use a randomization technique.
i. What are the claims being tested?
ii. The paragraph below describes the set up for such approach, if we were
to do it without using statistical software. Fill in the blanks with a number
or phrase, whichever is appropriate.
> We write *alive* on __________ cards representing patients who were
alive at the end of the study, and *dead* on _________ cards
representing patients who were not. Then, we shuffle these cards and split them
into two groups: one group of size _________ representing treatment, and
another group of size __________ representing control. We calculate the
difference between the proportion of *dead* cards in the treatment and
control groups (treatment - control) and record this value. We repeat this 100
times to build a distribution centered at _________. Lastly, we calculate
the fraction of simulations where the simulated differences in proportions are
_________. If this fraction is low, we conclude that it is unlikely to
have observed such an outcome by chance and that the null hypothesis should
be rejected in favor of the alternative.
iii. What do the simulation results shown below suggest about the effectiveness
of the transplant program?
```{r fig.height=3, fig.show="hold", message=FALSE, warning=FALSE, include=FALSE, out.width="50%", results='hide'}
# randomization -----------------------------------------------------
diffs <- DATA606::inference(heartTr$survived, heartTr$transplant,
success = "dead", order = c("treatment","control"),
est = "proportion", type = "ht", method = "simulation",
nsim = 100, null = 0, alternative = "twosided", simdist = TRUE,
seed = 95632)
```
\begin{center}
```{r, results='hide', echo=FALSE, message=FALSE, warning=FALSE, fig.show="hold", out.width="75%", fig.height=3}
# plot randomization distribution -----------------------------------
par(mar = c(3.6, 2.2, 1, 1), las = 1, mgp = c(2.5, 0.7, 0),
cex.axis = 1.5, cex.lab = 1.5)
values <- table(diffs)
plot(diffs, type = "n", xlim = c(-0.25, 0.25),
xlab = "simulated differences in proportions",
ylab = "", axes = FALSE, ylim = c(0, max(values)))
axis(1, at = seq(-0.25, 0.25, 0.05),
labels = c(-0.25, NA,-0.15, NA,-0.05, NA, 0.05, NA, 0.15, NA, 0.25))
for(i in 1:length(diffs)){
x <- diffs[i]
rec <- sum(diffs == x)
points(rep(x, rec), 1:rec, pch = 20, cex = 0.8, col = COL[1])
}
```
\end{center}