pwr_examples.Rmd

---
title: "Power calculation examples"
author: "M. Sonderegger and J. Kirby"
date: '2018-03-16'
output:
  pdf_document: default
  html_document: default
---

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


This document includes a couple examples of calculations with the `pwr` package, which you must have installed.
```{r}
library(pwr)
```

Example discussed in 2.4.1 in the text:

* To calculate power for a two-sample $t$ test, when sample size in each sample is $n=16$, effect size (Cohen's $d$) is 0.5, at significance level $\alpha=0.05$:
```{r}
pwr.t.test(n=16, d=0.5, sig.level = 0.05)
```

* Calculate what sample size would be needed to achieve power of $\beta = 0.8$ for this effect size and $\alpha$:
```{r}
pwr.t.test(d=0.5, sig.level = 0.05, power=0.8)
```