[英]Plotting power vs. effect size using R pwr package
I can successfully create plots of power vs. sample size in R using the pwr package.我可以使用 pwr package 在 R 中成功创建功率与样本大小的关系图。 Example code below.下面的示例代码。
library(pwr)
library(tidyverse)
plot.out <- pwr.t2n.test(n1=30, n2=30, d=0.5, alternative="two.sided")
#See output in link below
plot(plot.out)
I would like to create a similar plot -- a two-sample t-test in which effect size is on the y-axis and power is on the x-axis , with fixed sample sizes .我想创建一个类似的 plot -两个样本 t 检验,其中效应大小在 y 轴上,功率在 x 轴上,样本大小固定。
Is there a way to do this using pwr and/or the plot function?有没有办法使用 pwr 和/或 plot function 来做到这一点? Or would I have to unlist the plot.out object and use it somehow?或者我是否必须取消列出 plot.out object 并以某种方式使用它?
I'm still new to power curves in R.我对 R 中的功率曲线仍然不熟悉。 Thanks in advance for any advice.提前感谢您的任何建议。
In the code below the power is computed in a loop on effect size d_seq
.在下面的代码中,功率是在效果大小d_seq
的循环中计算的。 Then the power d
is extracted from the results list, a data.frame is created and plotted.然后从结果列表中提取幂d
,创建并绘制一个 data.frame。
library(pwr)
library(ggplot2)
d_seq <- seq(0, 2, by = 0.1)
pwr_list <- lapply(d_seq, function(d){
pwr.t2n.test(n1 = 30, n2 = 30,
d = d,
power = NULL,
sig.level = 0.05,
alternative = "two.sided")
})
pwr <- sapply(pwr_list, '[[', 'power')
dfpwr <- data.frame(power = pwr, effect.size = d_seq)
ggplot(dfpwr, aes(effect.size, power)) +
geom_point(size = 2, colour = "black") +
geom_line(size = 0.5, colour = "red") +
scale_y_continuous(labels = scales::percent) +
xlab("effect size") +
ylab(expression("test power =" ~ 1 - beta))
To draw a line where power is 80% and get the effect size, first compute the effect size from the pwr
vector by linear interpolation.要绘制一条功率为 80% 的线并获得效果大小,首先通过线性插值从pwr
向量计算效果大小。
pwr80 <- approx(x = pwr, y = d_seq, xout = 0.8)
Now create a label for geom_text
and plot it.现在为geom_text
和 plot 创建一个 label。
lbl80 <- paste("Power = 80%\n")
lbl80 <- paste(lbl80, "Effect size =", round(pwr80$y, 2))
ggplot(dfpwr, aes(effect.size, power)) +
geom_point(size = 2, colour = "black") +
geom_line(size = 0.5, colour = "red") +
geom_hline(yintercept = 0.8, linetype = "dotted") +
geom_text(x = pwr80$y, y = pwr80$x,
label = lbl80,
hjust = 1, vjust = -1) +
scale_y_continuous(labels = scales::percent) +
xlab("effect size") +
ylab(expression("test power =" ~ 1 - beta))
To also draw a vertical line, add要绘制垂直线,请添加
geom_vline(xintercept = pwr80$y, linetype = "dotted")
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