survival_analysis_example.Rmd

---
title: "survival_analysis_examples"
author: "Soumya Banerjee"
date: "27 August 2020"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

# Survival analysis

This is an R Markdown document that outlines some examples of survival analysis.

* Adapted from:
https://rviews.rstudio.com/2017/09/25/survival-analysis-with-r/

* www.stat.columbia.edu/~madigan/W2025/notes/survival.pdf

* http://data.princeton.edu/wws509/notes/

* https://en.wikipedia.org/wiki/Survival_function

* https://rpkgs.datanovia.com/survminer/index.html



## Load data

The variables in the veteran dataset are: 

* trt: 1=standard 2=test 

* celltype: 1=squamous, 2=small cell, 3=adeno, 4=large 

* time: survival time in days 

* status: censoring status 

* karno: Karnofsky performance score (100=good) 

* diagtime: months from diagnosis to randomization 

* age: in years 

* prior: prior therapy 0=no, 10=yes



```{r, include=FALSE}

library(survival)
library(ggplot2)
library(sqldf)
library(ggfortify)
library(ranger)
library(dplyr)
library(knitr)
library(rmarkdown)
library(survminer)

data("veteran")
head(veteran)

```

## Kaplan-Meier survival analysis

* this is a non-parametric model

* https://en.wikipedia.org/wiki/Kaplan?Meier_estimator


```{r, include=FALSE}

surv_object <- survival::Surv(time = veteran$time, event = veteran$status)

summary(surv_object)

as.data.frame.table(surv_object)

as.table(surv_object)

as.numeric(surv_object)

km_fit <- survival::survfit(formula = surv_object ~ 1, data = veteran)

summary(km_fit)

```



```{r, echo=FALSE}

autoplot(km_fit)

plot(km_fit)

```


## Kaplan-Meier survival analysis with covariates

```{r, include=FALSE}

surv_object <- survival::Surv(time = veteran$time, event = veteran$status)

km_fit_treatment <- survival::survfit(formula = surv_object ~ trt, data = veteran)

summary(km_fit_treatment)

```

```{r, echo=FALSE}

ggplot2::autoplot(km_fit_treatment)

```


## Fit a Cox-proportional hazards model

* this is a parametric model

* https://en.wikipedia.org/wiki/Proportional_hazards_model


```{r, include=FALSE}

surv_object <- survival::Surv(time = veteran$time, event = veteran$status)

cxph <- survival::coxph(formula = surv_object ~ trt + diagtime + age, data = veteran)

summary(cxph)

cxph_fit <- survival::survfit(cxph)

summary(cxph_fit)

summary(cxph_fit)$coef

# plot survival curve
plot(cxph_fit)

```


```{r, echo=FALSE}

ggplot2::autoplot(cxph_fit)

plot(cxph_fit)

```


## Better time to event plots

* https://rpkgs.datanovia.com/survminer/index.html


```{r, echo=FALSE}


###########################################
# Better plots for tiem to event analysis
###########################################

# from
# https://rpkgs.datanovia.com/survminer/index.html
# install.packages("survminer")
library("survminer")
library("survival")
fit <- survfit(Surv(time, status) ~ sex, data = lung)

ggsurvplot(fit, data = lung)

ggsurvplot(fit, data = lung, censor.shape="|", censor.size = 4)

ggsurvplot(
          fit, 
          data = lung, 
          size = 1,                 # change line size
          palette = 
            c("#E7B800", "#2E9FDF"),# custom color palettes
          conf.int = TRUE,          # Add confidence interval
          pval = TRUE,              # Add p-value
          risk.table = TRUE,        # Add risk table
          risk.table.col = "strata",# Risk table color by groups
          legend.labs = 
            c("Male", "Female"),    # Change legend labels
          risk.table.height = 0.25, # Useful to change when you have multiple groups
          ggtheme = theme_bw()      # Change ggplot2 theme
)

```



## Cox proportional hazards models

* https://rpkgs.datanovia.com/survminer/index.html


```{r, echo=FALSE}

fit <- survival::coxph(formula = Surv(time = time, event = status) ~ sex + age, data = lung)
survminer::ggadjustedcurves(fit = fit, data = lung, variable = "sex")

```


## Diagnostics

* https://rpkgs.datanovia.com/survminer/index.html


```{r, echo=FALSE}

fit <- survival::coxph(formula = Surv(time = time, event = status) ~ sex + age, data = lung)
ftest <- survival::cox.zph(fit = fit)

# test assumptions of proportional hazards model
survminer::ggcoxzph(fit = ftest)
survminer::ggcoxdiagnostics(fit = fit, type = "schoenfeld", ox.scale = "time")
survminer::ggcoxdiagnostics(fit = fit, type = "deviance",   ox.scale = "linear.predictions")

survminer::ggadjustedcurves(fit = fit, data = lung, variable = "sex")

```


## Visualization of parameters and hazard ratios (HR)

* https://rpkgs.datanovia.com/survminer/index.html


```{r, echo=FALSE}

summary(fit)

survminer::ggforest(model = fit, data = lung)

```


## Use strata to fit models

* This fits a separate baseline hazard for each factor (here it is gender)

* https://stats.stackexchange.com/questions/256148/stratification-in-cox-model


```{r, echo=FALSE}

fit <- survival::coxph(formula = Surv(time = time, event = status) ~ sex + age + strata(sex), data = lung)
summary(fit)

```

## Better statistics


```{r, echo=FALSE}

# advanced analysis
# from http://egret.psychol.cam.ac.uk/not_advertised/RNC/annabel_alzd_dlb_survival.R

DOWNLOAD_DIR <- "download"
OUTPUT_DIR <- "output"
dir.create(DOWNLOAD_DIR, showWarnings=FALSE)
dir.create(OUTPUT_DIR, showWarnings=FALSE)

RESULTS_FILENAME <- sprintf("%s/%s", OUTPUT_DIR, "results.txt")

surv_object <- survival::Surv(time = veteran$time, event = veteran$status)

cxph <- survival::coxph(formula = surv_object ~ trt + diagtime + age, data = veteran)

summary(cxph)

cxph_fit <- survival::survfit(cxph)

summary(cxph_fit)


# list[p1, median1] =  survival_info(survfit_or_coxph = cxph, newdata = veteran, strata = veteran$celltype)
# save_figure(p1, "survival_dx.pdf", "Survival by diagnosis only")
# debug_quantity(median1, filename=RESULTS_FILENAME, print_only=TRUE)


```









## References

* https://rviews.rstudio.com/2017/09/25/survival-analysis-with-r/, URL accessed 01-01-2019

* Kartsonaki C (2016) Survival analysis. Diagnostic Histopathol 22: 263?270.

* www.stat.columbia.edu/~madigan/W2025/notes/survival.pdf, URL accessed 01-01-2019

* http://data.princeton.edu/wws509/notes/, URL accessed 01-01-2019

* https://rpkgs.datanovia.com/survminer/index.html, URL accessed 01-09-2019