---
title: "Biostatistics III in R"
author:
- Code by Annika Tillander, Andreas Karlsson and Mark Clements
output:
  prettydoc::html_pretty:
    theme: cayman
    highlight: github
---


# Exercise 2. Comparing survival proportions and mortality rates by stage for cause-specific and all-cause survival #
	

```{r setup, cache=FALSE, message=FALSE, echo=FALSE}
library('knitr')
read_chunk('../q2.R')
opts_chunk$set(cache=FALSE, fig.width=10, fig.height=6, results='hide', fig.keep='none')
```

The purpose of this exercise is to study survival of the patients
    using two alternative measures --- survival proportions and
    mortality rates. A second purpose is to study the difference between
    cause-specific and all-cause survival.


Load dependencies

```{r loadDependencies, message=FALSE}
```

We start by listing the first few observations to get an idea about the data. We then define two 1/0 variables for the events that we are interested in.

```{r loadPreprocess, results='markup'}
```

## (a) Plot estimates of the survivor function and hazard function by stage ##

We now tabulate the distribution of the melanoma patients by cancer stage at diagnosis.

```{r a_tabulate}
```

We then plot the survival and hazards by stage. Does it appear that stage is associated with patient survival?

```{r a_plotSurv}
```

As an extension, this could be calculated using the `bshazard` package, with plotting using either `ggplot2` or `lattice` packages.

## (b) Estimate the mortality rates for each stage using, for example, the `survRate` command ##

```{r b_crudeRates}
```

What are the units of the estimated rates? The `survRate` function, as the name suggests, is used to
        estimates rates. Look at the help pages if you are not familiar
        with the function (e.g. `?survRate` or `help(survRate)`).


## (c) ##
If you haven’t already done so, estimate the mortality rates for each stage per person-year and per 1000 person-years of follow-up.

## (d) ##

Study whether survival is different for males and females (both
        by plotting the survivor function and by tabulating
        mortality rates).
Is there a difference in survival between males and females? If
        yes, is the difference present throughout the follow up?

## (e) ##

The plots you made above were based on cause-specific survival
(i.e., only deaths due to cancer are counted as events, deaths
due to other causes are censored). In the next part of this
question we will estimate all-cause survival (i.e., any death is
counted as an event). First, however, study the coding of vital
status and tabulate vital status by age group.

How many patients die of each cause? Does the distribution of
cause of death depend on age?


```{r e_tabByAge}
```

## (f) ##

To get all-cause survival, specify all deaths (both cancer
and other) as events.

Now plot the survivor proportion for all-cause survival
by stage. We name the graph to be able to separate them in the
graph window. Is the survivor proportion different compared to
the cause-specific survival you estimated above? Why?

## (g) ##

It is more common to die from a cause other than cancer in
older ages. How does this impact the survivor proportion for
different stages? Compare cause-specific and all-cause survival
by plotting the survivor proportion by stage for the oldest age
group (75+ years) for both cause-specific and
all-cause survival.

## (h) ##

Now estimate both cancer-specific and all-cause survival for
        each age group.
